/* El Estudiante · Propuesta A «El cuaderno que se escribe solo» · sistema Cuaderno v1.0 */

@font-face { font-family: 'Source Serif 4'; src: url('../fuentes/source-serif-4.woff2') format('woff2'); font-weight: 200 900; font-style: normal; font-display: swap; }
@font-face { font-family: 'Source Serif 4'; src: url('../fuentes/source-serif-4-italic.woff2') format('woff2'); font-weight: 200 900; font-style: italic; font-display: swap; }
@font-face { font-family: 'Manrope'; src: url('../fuentes/manrope.woff2') format('woff2'); font-weight: 200 800; font-display: swap; }
@font-face { font-family: 'JetBrains Mono'; src: url('../fuentes/jetbrains-mono.woff2') format('woff2'); font-weight: 100 800; font-display: swap; }

:root {
  --pizarra: #1E3D33;
  --pizarra-prof: #15302A;
  --papel: #F5F1E3;
  --papel-osc: #EDE7D3;
  --blanco: #FCFCFC;
  --terracota: #B5523B;
  --terracota-osc: #9E4330;
  --terracota-clara: #E08A70;
  --salvia: #7A9D82;
  --madera: #5D4037;
  --subrayador: rgba(122, 157, 130, .55);
  --cuadricula: rgba(30, 61, 51, .075);
  --borde: rgba(30, 61, 51, .18);
  --f-tit: 'Source Serif 4', Georgia, serif;
  --f-txt: 'Manrope', 'Segoe UI', system-ui, sans-serif;
  --f-mono: 'JetBrains Mono', ui-monospace, Consolas, monospace;
  --paso: 28px;
  --margen: clamp(28px, 6vw, 88px);
  --sombra: 6px 6px 0 var(--pizarra);
  --sombra-p: 4px 4px 0 var(--pizarra);
  --ancho: 1240px;
  --ease: cubic-bezier(.2, .7, .1, 1);
}

*, *::before, *::after { box-sizing: border-box; }
html { scroll-behavior: smooth; -webkit-text-size-adjust: 100%; }
body {
  margin: 0;
  background-color: var(--papel);
  background-image:
    linear-gradient(var(--cuadricula) 1px, transparent 1px),
    linear-gradient(90deg, var(--cuadricula) 1px, transparent 1px);
  background-size: var(--paso) var(--paso);
  color: var(--pizarra);
  font: 400 1.0625rem/1.65 var(--f-txt);
  overflow-x: hidden;
}
/* Línea de margen terracota de todo el cuaderno */
body::before {
  content: ''; position: fixed; top: 0; bottom: 0; left: var(--margen); width: 2px;
  background: var(--terracota); opacity: .75; z-index: 0; pointer-events: none;
}
img { max-width: 100%; display: block; }
a { color: inherit; }
::selection { background: var(--subrayador); }
:focus-visible { outline: 2.5px solid var(--terracota); outline-offset: 3px; border-radius: 4px; }

.cont { width: min(var(--ancho), 100% - 2 * var(--margen) - 32px); margin-left: calc(var(--margen) + 32px); margin-right: auto; position: relative; z-index: 1; }
@media (min-width: 1500px) { .cont { margin-left: auto; } }

.etq { font: 500 .78rem/1.3 var(--f-mono); letter-spacing: .14em; text-transform: uppercase; color: var(--terracota-osc); }
.mk { background: linear-gradient(transparent 56%, var(--subrayador) 56%) no-repeat 0 0 / 0% 100%; transition: background-size .9s var(--ease); padding: 0 .08em; }
.mk.on, .vis .mk { background-size: 100% 100%; }
mark { background: linear-gradient(transparent 56%, var(--subrayador) 56%); color: inherit; padding: 0 .08em; }

/* ---------- Botones ---------- */
.btn {
  display: inline-flex; align-items: center; gap: .55em; padding: .8em 1.3em; border-radius: 10px;
  font: 700 .98rem/1 var(--f-txt); text-decoration: none; border: 2px solid var(--pizarra); cursor: pointer;
  transition: transform .18s var(--ease), box-shadow .18s var(--ease), background .2s;
}
.btn svg { width: 1.15em; height: 1.15em; fill: currentColor; }
.btn--pri { background: var(--pizarra); color: var(--papel); box-shadow: var(--sombra-p); }
.btn--pri:hover { transform: translate(-2px, -2px); box-shadow: 6px 6px 0 var(--terracota); }
.btn--sec { background: var(--blanco); color: var(--pizarra); box-shadow: var(--sombra-p); }
.btn--sec:hover { transform: translate(-2px, -2px); box-shadow: 6px 6px 0 var(--pizarra); }
.btn--yt { background: var(--terracota); border-color: var(--terracota); color: var(--blanco); border-radius: 999px; padding: .62em 1.1em; font-size: .9rem; }
.btn--yt:hover { background: var(--terracota-osc); border-color: var(--terracota-osc); }

/* ---------- Cabecera ---------- */
.cab { position: sticky; top: 0; z-index: 50; transition: background .3s, box-shadow .3s; }
.cab.scrolled { background: rgba(245, 241, 227, .9); backdrop-filter: blur(10px); box-shadow: 0 1px 0 var(--borde); }
.cab .cont { display: flex; align-items: center; justify-content: space-between; gap: 24px; height: 76px; }
.cab__logo img { height: 40px; width: auto; }
.cab nav { display: flex; gap: clamp(14px, 2.4vw, 34px); align-items: center; }
.cab nav a:not(.btn) { text-decoration: none; font-weight: 600; font-size: .95rem; position: relative; }
.cab nav a:not(.btn)::after { content: ''; position: absolute; left: 0; right: 0; bottom: -2px; height: 8px; background: var(--subrayador); transform: scaleX(0); transform-origin: left; transition: transform .35s var(--ease); z-index: -1; }
.cab nav a:not(.btn):hover::after { transform: scaleX(1); }
@media (max-width: 860px) { .cab nav a:not(.btn) { display: none; } .cab__logo img { height: 34px; } }

/* ---------- Héroe ---------- */
.heroe { position: relative; min-height: calc(100vh - 76px); min-height: calc(100svh - 76px); display: flex; align-items: center; padding: 40px 0 80px; }
#tinta { position: absolute; inset: 0; width: 100%; height: 100%; z-index: 0; pointer-events: none; }
.heroe .cont { display: grid; grid-template-columns: 1.05fr .95fr; gap: clamp(32px, 5vw, 80px); align-items: center; }
.heroe h1 { font: 800 clamp(2.5rem, 5vw, 5.2rem)/.98 var(--f-tit); letter-spacing: -.025em; margin: .35em 0 .4em; }
.heroe h1 .linea { display: block; overflow: hidden; padding-bottom: .06em; white-space: nowrap; }
.heroe h1 .linea > span { display: inline-block; transform: translateY(105%); animation: subir .9s var(--ease) forwards; }
.heroe h1 .linea:nth-child(2) > span { animation-delay: .12s; }
.heroe h1 .linea:nth-child(3) > span { animation-delay: .24s; }
.heroe h1 em { font-style: italic; font-weight: 700; color: var(--terracota); }
@keyframes subir { to { transform: none; } }
.heroe__lead { font-size: clamp(1.05rem, 1.5vw, 1.25rem); max-width: 34em; color: var(--madera); margin: 0 0 2em; opacity: 0; animation: aparecer .8s .55s forwards; }
.heroe__acc { display: flex; flex-wrap: wrap; gap: 14px; opacity: 0; animation: aparecer .8s .7s forwards; }
@keyframes aparecer { from { opacity: 0; transform: translateY(12px); } to { opacity: 1; transform: none; } }
.heroe .etq { opacity: 0; animation: aparecer .6s .1s forwards; display: inline-flex; gap: .8em; align-items: center; }
.heroe .etq::before { content: ''; width: 28px; height: 2px; background: var(--terracota); }

/* Mesa del héroe: polaroid + fichas de fórmulas */
.mesa { position: relative; aspect-ratio: 1 / 1.02; perspective: 1400px; }
.mesa > * { position: absolute; transition: transform .5s var(--ease); will-change: transform; }
.polaroid { background: var(--blanco); padding: 14px 14px 56px; box-shadow: 0 22px 50px rgba(30, 61, 51, .22), 0 2px 0 rgba(0,0,0,.04); }
.polaroid::before { content: ''; position: absolute; top: -16px; left: 50%; width: 120px; height: 34px; margin-left: -60px; background: rgba(122, 157, 130, .62); transform: rotate(-3deg); }
.polaroid figcaption { position: absolute; left: 0; right: 0; bottom: 14px; text-align: center; font: italic 600 1.15rem/1 var(--f-tit); color: var(--madera); }
.mesa .polaroid { width: 70%; top: 2%; right: 2%; transform: rotate(3.5deg); }
.ficha {
  background: var(--blanco); border: 2px solid var(--pizarra); border-radius: 10px; box-shadow: var(--sombra);
  padding: 18px 22px; font-size: clamp(1rem, 1.6vw, 1.35rem); color: var(--pizarra);
}
.ficha .etq { display: block; margin-bottom: 6px; font-size: .66rem; }
.mesa .ficha--1 { left: -2%; bottom: 21%; transform: rotate(-4deg); z-index: 3; }
.mesa .ficha--2 { left: 6%; top: 8%; transform: rotate(-9deg); z-index: 1; font-size: clamp(.9rem, 1.3vw, 1.1rem); }
.mesa .ficha--3 { right: -3%; bottom: -4%; transform: rotate(5deg); z-index: 2; font-size: clamp(.95rem, 1.4vw, 1.2rem); }
.escribe { clip-path: inset(-20% 100% -20% 0); }
.escribe.on { animation: escribir 1.6s var(--ease) forwards; }
@keyframes escribir { to { clip-path: inset(-20% -2% -20% 0); } }
.sello {
  width: 128px; height: 128px; border-radius: 50%; border: 4px solid var(--terracota); color: var(--terracota);
  display: grid; place-items: center; text-align: center; font: 800 1.45rem/1 var(--f-tit); letter-spacing: .04em;
  background: rgba(252, 252, 252, .55); mix-blend-mode: multiply;
}
.sello small { display: block; font: 600 .44rem/1.25 var(--f-mono); letter-spacing: .12em; margin-top: 5px; text-transform: uppercase; }
.sello::after { content: ''; position: absolute; inset: 7px; border-radius: 50%; border: 1.5px dashed var(--terracota); }
.mesa .sello { left: 1%; top: 37%; z-index: 4; transform: rotate(-14deg) scale(2.4); opacity: 0; }
.mesa .sello.on { animation: estampar .5s cubic-bezier(.3, 1.6, .5, 1) forwards; }
@keyframes estampar { 0% { opacity: 0; transform: rotate(-14deg) scale(2.4); } 60% { opacity: 1; } 100% { opacity: .92; transform: rotate(-14deg) scale(1); } }
.lapiz { position: absolute; width: 46px; height: 46px; pointer-events: none; z-index: 6; opacity: 0; transition: opacity .3s; }
.lapiz.on { opacity: 1; }
@media (max-width: 920px) {
  .heroe .cont { grid-template-columns: 1fr; }
  .mesa { max-width: 520px; width: 100%; margin: 10px auto 0; }
}

/* ---------- Cinta de fórmulas ---------- */
.cinta { position: relative; z-index: 2; margin: 0 -2vw; transform: rotate(-1.6deg); background: var(--salvia); color: var(--pizarra-prof); overflow: hidden; padding: 16px 0; box-shadow: 0 10px 30px rgba(30,61,51,.12); }
.cinta--2 { transform: rotate(1.2deg); background: var(--pizarra); color: var(--papel); margin-top: -26px; }
.cinta__pista { display: flex; gap: 64px; width: max-content; animation: deslizar 46s linear infinite; font-size: 1.35rem; align-items: center; }
.cinta--2 .cinta__pista { animation-direction: reverse; animation-duration: 60s; }
.cinta__pista > span { display: inline-flex; align-items: center; gap: 64px; white-space: nowrap; }
.cinta__pista > span::after { content: 'Σ'; font: 700 1.1rem var(--f-tit); color: var(--terracota); }
.cinta--2 .cinta__pista > span::after { color: var(--terracota-clara); }
@keyframes deslizar { to { transform: translateX(-50%); } }

/* ---------- Secciones ---------- */
.sec { padding: clamp(80px, 11vw, 150px) 0; position: relative; }
.sec__cab { max-width: 760px; margin-bottom: clamp(40px, 5vw, 64px); }
.sec__cab h2 { font: 800 clamp(2.2rem, 4.6vw, 3.8rem)/1.02 var(--f-tit); letter-spacing: -.02em; margin: .3em 0 .35em; }
.sec__cab p { font-size: 1.15rem; color: var(--madera); margin: 0; max-width: 36em; }
.nota-margen {
  position: absolute; left: calc(-1 * var(--margen) - 32px + 8px); width: calc(var(--margen) + 8px); text-align: right;
  font: 500 .72rem/1.3 var(--f-mono); letter-spacing: .08em; text-transform: uppercase; color: var(--terracota); padding-right: 22px;
}
@media (max-width: 700px) { .nota-margen { display: none; } }

/* ---------- Demostración que se escribe sola (scroll) ---------- */
.prueba { height: 560vh; position: relative; }
.prueba__pin { position: sticky; top: 0; height: 100vh; height: 100svh; display: flex; align-items: center; overflow: hidden; }
.prueba__hoja { display: grid; grid-template-columns: 1fr 330px; gap: clamp(24px, 4vw, 64px); align-items: start; width: 100%; }
.prueba__titulo { font: 800 clamp(1.8rem, 3.6vw, 3rem)/1.05 var(--f-tit); margin: .2em 0 .7em; letter-spacing: -.015em; }
.prueba ol { list-style: none; margin: 0; padding: 0; counter-reset: paso; }
.prueba li {
  position: relative; display: flex; align-items: center; min-height: calc(var(--paso) * 2.1);
  font-size: clamp(1.1rem, 1.9vw, 1.55rem); counter-increment: paso;
}
.prueba li > span { clip-path: inset(-40% calc((1 - var(--p, 0)) * 100%) -40% 0); }
.prueba li > .txt { clip-path: inset(-40% calc((1 - min(1, var(--p, 0) * 1.4 - .4)) * 100%) -40% 0); }
.prueba li .txt { font: 500 .95em/1.35 var(--f-txt); color: var(--madera); margin-left: .8em; }
.prueba li .txt b { color: var(--pizarra); }
.prueba li::before {
  content: 'Paso ' counter(paso); position: absolute; right: calc(100% + 46px); width: 120px; text-align: right;
  font: 500 .7rem/1 var(--f-mono); letter-spacing: .1em; text-transform: uppercase; color: var(--terracota);
  opacity: min(1, calc(var(--p, 0) * 3)); transform: translateX(calc((1 - min(1, var(--p, 0) * 3)) * -10px));
}
.prueba li.final .katex { color: var(--terracota); }
.prueba__lado { display: flex; flex-direction: column; gap: 28px; align-items: stretch; position: relative; }
.hipotesis { position: relative; background: var(--blanco); border: 2px solid var(--pizarra); border-radius: 10px; box-shadow: var(--sombra); padding: 18px 22px; transform: rotate(1.5deg); }
.hipotesis .etq { display: block; margin-bottom: 6px; }
.hipotesis .katex { font-size: 1.6em; }
.hipotesis > svg { position: absolute; inset: -8px; width: calc(100% + 16px); height: calc(100% + 16px); overflow: visible; pointer-events: none; }
.hipotesis > svg path { fill: none; stroke: var(--terracota); stroke-width: 5; stroke-linecap: round; stroke-dasharray: 1; stroke-dashoffset: calc(1 - var(--tacha, 0)); }
.prueba .sello { position: relative; margin: 0 auto; transform: rotate(-12deg) scale(calc(2.6 - var(--s, 0) * 1.6)); opacity: var(--s, 0); }
.prueba__barra { position: absolute; left: calc(-1 * var(--margen) - 32px + var(--margen) - 4px); top: 0; width: 10px; height: 100%; }
.prueba__barra span { position: absolute; left: 0; top: 0; width: 10px; height: calc(var(--prog, 0) * 100%); background: var(--salvia); border-radius: 0 0 6px 6px; opacity: .8; }
.prueba__fin { display: flex; gap: 12px; flex-wrap: wrap; margin-top: 30px; opacity: var(--s, 0); transform: translateY(calc((1 - var(--s, 0)) * 16px)); }
.prueba__ayuda { font: 500 .78rem/1.3 var(--f-mono); color: var(--madera); letter-spacing: .06em; margin-top: 18px; opacity: calc(1 - var(--prog, 0) * 6); }
@media (max-width: 900px) {
  .prueba__hoja { grid-template-columns: 1fr; }
  .prueba__lado { flex-direction: row; flex-wrap: wrap; order: -1; align-items: center; }
  .prueba .sello { width: 92px; height: 92px; font-size: 1.05rem; margin: 0; }
  .prueba li { min-height: 46px; }
  .prueba li::before { display: none; }
}

/* ---------- Fichas de demostraciones ---------- */
.fichas { display: grid; grid-template-columns: repeat(3, 1fr); gap: clamp(22px, 3vw, 40px); }
@media (max-width: 1020px) { .fichas { grid-template-columns: 1fr 1fr; } }
@media (max-width: 680px) { .fichas { grid-template-columns: 1fr; } }
.demo {
  position: relative; background: var(--blanco); border: 2px solid var(--pizarra); border-radius: 12px; box-shadow: var(--sombra);
  padding: 18px 18px 22px; display: flex; flex-direction: column; gap: 14px;
  transform: rotate(var(--r, 0deg)); transition: transform .35s var(--ease), box-shadow .35s var(--ease);
}
.demo:nth-child(1) { --r: -1.2deg; } .demo:nth-child(2) { --r: .9deg; } .demo:nth-child(3) { --r: -.6deg; } .demo:nth-child(4) { --r: 1.1deg; }
.demo:hover { transform: rotate(0) translate(-3px, -6px); box-shadow: 10px 12px 0 var(--pizarra); }
.demo__mini { position: relative; border-radius: 6px; overflow: hidden; aspect-ratio: 16 / 9; border: 1.5px solid var(--borde); }
.demo__mini img { width: 100%; height: 100%; object-fit: cover; transition: transform .6s var(--ease); }
.demo:hover .demo__mini img { transform: scale(1.045); }
.demo__mini::before { content: ''; position: absolute; top: -6px; right: 16%; width: 84px; height: 26px; background: rgba(122, 157, 130, .7); transform: rotate(4deg); z-index: 2; }
.demo__num { display: flex; justify-content: space-between; align-items: baseline; }
.demo__num .n { font: 800 2.6rem/1 var(--f-tit); color: var(--terracota); }
.demo h3 { font: 800 1.65rem/1.08 var(--f-tit); margin: 0; letter-spacing: -.01em; }
.demo h3 span { background: linear-gradient(transparent 58%, var(--subrayador) 58%) no-repeat 0 0 / 0% 100%; transition: background-size .5s var(--ease); }
.demo:hover h3 span { background-size: 100% 100%; }
.demo p { margin: 0; color: var(--madera); font-size: .98rem; }
.demo__formula { background: var(--papel); border: 1.5px dashed var(--borde); border-radius: 8px; padding: 12px; text-align: center; font-size: 1.12rem; overflow-x: auto; overflow-y: hidden; }
.demo__acc { display: flex; gap: 8px; flex-wrap: wrap; margin-top: auto; }
.chip {
  display: inline-flex; align-items: center; gap: 6px; padding: 7px 12px; border-radius: 999px; border: 1.5px solid var(--pizarra);
  font: 700 .82rem/1 var(--f-txt); text-decoration: none; background: var(--blanco); transition: background .2s, color .2s;
}
.chip svg { width: 14px; height: 14px; fill: currentColor; }
.chip:hover { background: var(--pizarra); color: var(--papel); }
.chip--pri { background: var(--pizarra); color: var(--papel); }
.chip--pri:hover { background: var(--terracota); border-color: var(--terracota); }
.chip--off { opacity: .55; pointer-events: none; border-style: dashed; }
.pronto { position: absolute; z-index: 3; top: 50%; left: 50%; transform: translate(-50%, -50%) rotate(-10deg); border: 3px solid var(--terracota); color: var(--terracota); background: rgba(252, 252, 252, .9); padding: 8px 16px; border-radius: 8px; font: 800 1rem/1 var(--f-mono); letter-spacing: .12em; text-transform: uppercase; }
.demo--vacia { background: transparent; border-style: dashed; box-shadow: none; justify-content: center; align-items: flex-start; min-height: 320px; }
.demo--vacia:hover { box-shadow: none; }
.demo--vacia h3 { color: var(--madera); }

/* ---------- Shorts ---------- */
.shorts { display: grid; grid-template-columns: 1.1fr 1fr 1fr; gap: clamp(22px, 3vw, 44px); align-items: center; }
@media (max-width: 860px) { .shorts { grid-template-columns: 1fr 1fr; } .shorts .sec__cab { grid-column: 1 / -1; } }
.short { position: relative; display: block; text-decoration: none; background: var(--blanco); padding: 10px 10px 54px; box-shadow: 0 18px 40px rgba(30, 61, 51, .2); transform: rotate(var(--r, 2deg)); transition: transform .35s var(--ease); }
.short:nth-of-type(2) { --r: -2.5deg; }
.short:hover { transform: rotate(0) scale(1.03); }
.short__img { aspect-ratio: 9 / 14; overflow: hidden; background: var(--pizarra); }
.short__img img { width: 100%; height: 100%; object-fit: cover; }
.short b { position: absolute; left: 14px; right: 14px; bottom: 16px; font: italic 700 1.1rem/1.1 var(--f-tit); color: var(--pizarra); }
.short::after { content: '▶ Short'; position: absolute; top: 20px; left: 20px; background: var(--terracota); color: var(--blanco); font: 700 .7rem/1 var(--f-mono); letter-spacing: .1em; padding: 6px 9px; border-radius: 999px; }

/* ---------- Método (tres pasos) ---------- */
.metodo { display: grid; grid-template-columns: repeat(3, 1fr); gap: 0; border-top: 2px solid var(--pizarra); }
@media (max-width: 860px) { .metodo { grid-template-columns: 1fr; } }
.metodo > div { padding: 30px 28px 10px 0; border-right: 1.5px dashed var(--borde); padding-left: 28px; }
.metodo > div:first-child { padding-left: 0; }
.metodo > div:last-child { border-right: 0; }
.metodo .n { font: 800 4.2rem/1 var(--f-tit); color: transparent; -webkit-text-stroke: 1.6px var(--terracota); }
.metodo h3 { font: 800 1.45rem/1.15 var(--f-tit); margin: .4em 0 .3em; }
.metodo p { color: var(--madera); margin: 0; }

/* ---------- Sobre el canal ---------- */
.sobre { display: grid; grid-template-columns: .8fr 1.2fr; gap: clamp(32px, 6vw, 96px); align-items: center; }
@media (max-width: 860px) { .sobre { grid-template-columns: 1fr; } }
.sobre .polaroid { position: relative; transform: rotate(-3deg); max-width: 420px; }
.sobre blockquote { margin: 0 0 .6em; font: italic 700 clamp(2rem, 4.2vw, 3.4rem)/1.08 var(--f-tit); letter-spacing: -.015em; }
.sobre p { font-size: 1.12rem; color: var(--madera); max-width: 34em; }

/* ---------- Pizarra final ---------- */
.pizarra { position: relative; background: var(--pizarra); color: var(--papel); border-radius: 18px; padding: clamp(48px, 8vw, 110px) clamp(28px, 6vw, 90px); overflow: hidden; box-shadow: 0 0 0 10px #6b4f3a, 0 0 0 12px #4e3829, 0 30px 60px rgba(0,0,0,.25); }
.pizarra::before { content: ''; position: absolute; inset: 0; background: radial-gradient(ellipse at 30% 20%, rgba(255,255,255,.08), transparent 60%); pointer-events: none; }
.pizarra h2 { font: 800 clamp(2.4rem, 6vw, 5rem)/1 var(--f-tit); margin: 0 0 .3em; letter-spacing: -.02em; }
.pizarra h2 em { color: var(--terracota-clara); }
.pizarra p { font-size: 1.15rem; max-width: 34em; color: rgba(245, 241, 227, .82); }
.pizarra .btn--sec { margin-top: 18px; }
.pizarra__formulas { position: absolute; right: 4%; top: 10%; bottom: 10%; width: 44%; color: rgba(252, 252, 252, .13); font-size: 1.5rem; display: flex; flex-direction: column; justify-content: space-around; align-items: flex-end; pointer-events: none; }
@media (max-width: 860px) { .pizarra__formulas { display: none; } }

/* ---------- Pie ---------- */
.pie { padding: 50px 0 60px; font-size: .9rem; color: var(--madera); }
.pie .cont { display: flex; justify-content: space-between; gap: 20px; flex-wrap: wrap; align-items: center; }
.pie a { font-weight: 600; text-decoration: none; }
.pie a:hover { text-decoration: underline; text-decoration-color: var(--terracota); text-decoration-thickness: 2px; }
.pie nav { display: flex; gap: 22px; flex-wrap: wrap; }

/* ---------- Aparición al hacer scroll ---------- */
.rv { opacity: 0; transform: translateY(26px); transition: opacity .8s var(--ease), transform .8s var(--ease); }
.rv.vis { opacity: 1; transform: none; }
.fichas .rv:nth-child(2) { transition-delay: .1s; } .fichas .rv:nth-child(3) { transition-delay: .2s; } .fichas .rv:nth-child(4) { transition-delay: .3s; }
.demo.rv.vis { transform: rotate(var(--r, 0deg)); }
.demo.rv.vis:hover { transform: rotate(0) translate(-3px, -6px); }

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after { animation-duration: .01ms !important; animation-delay: 0s !important; transition-duration: .01ms !important; }
  .cinta__pista { animation: none; }
  .escribe { clip-path: none; }
}

/* =========================================================================
   Páginas de apuntes
   ========================================================================= */
.ap-heroe { padding: clamp(40px, 6vw, 80px) 0 clamp(30px, 4vw, 50px); }
.ap-heroe .cont { display: grid; grid-template-columns: 1.1fr .9fr; gap: clamp(28px, 5vw, 70px); align-items: center; }
@media (max-width: 960px) { .ap-heroe .cont { grid-template-columns: 1fr; } }
.ap-heroe .migas { font: 500 .78rem/1 var(--f-mono); letter-spacing: .08em; color: var(--madera); }
.ap-heroe .migas a { text-decoration: none; border-bottom: 1.5px solid var(--salvia); }
.ap-heroe h1 { font: 800 clamp(2.6rem, 5.8vw, 5rem)/1 var(--f-tit); letter-spacing: -.025em; margin: .3em 0 .25em; }
.ap-heroe .num { font: 800 1.2rem/1 var(--f-mono); color: var(--terracota); }
.ap-heroe .gancho { font: italic 500 clamp(1.15rem, 1.8vw, 1.45rem)/1.4 var(--f-tit); color: var(--madera); margin: 0 0 1.2em; max-width: 30em; }
.ap-meta { display: flex; flex-wrap: wrap; gap: 8px; margin-bottom: 22px; }
.ap-meta span { font: 500 .78rem/1 var(--f-mono); padding: 7px 10px; border: 1.5px solid var(--borde); border-radius: 6px; background: rgba(252,252,252,.6); }
.ap-acc { display: flex; gap: 12px; flex-wrap: wrap; }
.ap-heroe .formula-grande { margin-top: 26px; font-size: clamp(1.2rem, 2.2vw, 1.7rem); overflow-x: auto; overflow-y: hidden; }

.video { position: relative; aspect-ratio: 16 / 9; border-radius: 10px; overflow: hidden; background: var(--pizarra); border: 2px solid var(--pizarra); box-shadow: var(--sombra); }
.video img, .video iframe { width: 100%; height: 100%; object-fit: cover; border: 0; display: block; }
.video__play { position: absolute; inset: 0; margin: auto; width: 84px; height: 84px; border-radius: 50%; border: 0; background: var(--terracota); cursor: pointer; display: grid; place-items: center; box-shadow: 0 10px 30px rgba(0,0,0,.3); transition: transform .25s var(--ease), background .2s; }
.video__play svg { width: 34px; height: 34px; fill: var(--blanco); margin-left: 4px; }
.video:hover .video__play { transform: scale(1.1); background: var(--terracota-osc); }
.video__dur { position: absolute; right: 10px; bottom: 10px; background: rgba(21,48,42,.85); color: var(--papel); font: 600 .75rem/1 var(--f-mono); padding: 5px 7px; border-radius: 4px; }
.video__pronto { position: absolute; left: 50%; top: 50%; transform: translate(-50%, -50%) rotate(-8deg); border: 3px solid var(--terracota-clara); color: var(--terracota-clara); background: rgba(21,48,42,.85); padding: 10px 18px; border-radius: 8px; font: 800 .95rem/1 var(--f-mono); letter-spacing: .1em; text-transform: uppercase; white-space: nowrap; }
.ap-heroe .video { transform: rotate(1.2deg); }

.ap-cuerpo { display: grid; grid-template-columns: minmax(0, 1fr) 280px; gap: clamp(30px, 5vw, 80px); padding-bottom: 80px; align-items: start; }
.ap-lateral { position: sticky; top: 100px; display: flex; flex-direction: column; gap: 20px; }
@media (max-width: 1060px) { .ap-cuerpo { grid-template-columns: 1fr; } .ap-lateral { display: none; } }
.toc { background: var(--blanco); border: 2px solid var(--pizarra); border-radius: 10px; box-shadow: var(--sombra-p); padding: 16px 0 10px; }
.toc .etq { padding: 0 18px 8px; display: block; }
.toc ol { list-style: none; margin: 0; padding: 0; }
.toc a { display: block; padding: 7px 18px; text-decoration: none; font-size: .9rem; line-height: 1.3; border-left: 4px solid transparent; transition: background .2s, border-color .2s; }
.toc a:hover { background: var(--papel); }
.toc a.activo { border-left-color: var(--terracota); background: linear-gradient(90deg, rgba(122,157,130,.25), transparent); }
.toc__margen { display: block; font: 500 .62rem/1.2 var(--f-mono); letter-spacing: .1em; text-transform: uppercase; color: var(--terracota-osc); }
.toc__titulo { font-weight: 600; }
.pdfcard { display: flex; gap: 14px; align-items: center; text-decoration: none; background: var(--pizarra); color: var(--papel); border-radius: 10px; padding: 16px 18px; box-shadow: 4px 4px 0 var(--terracota); transition: transform .2s var(--ease); }
.pdfcard:hover { transform: translate(-2px, -2px); }
.pdfcard svg { width: 34px; height: 34px; flex: none; fill: var(--terracota-clara); }
.pdfcard b { display: block; font: 700 1rem/1.2 var(--f-tit); }
.pdfcard small { display: block; margin-top: 4px; font: 500 .72rem/1.35 var(--f-mono); opacity: .75; }

/* Contenido de los apuntes */
.apuntes { font-size: 1.1rem; max-width: 760px; }
.apuntes .entradilla { font: 500 1.25rem/1.55 var(--f-tit); color: var(--pizarra); margin: 0 0 1.4em; }
.apuntes section { position: relative; padding-top: 30px; scroll-margin-top: 90px; }
.apuntes section::before {
  content: attr(data-margen); position: absolute; top: 40px; right: calc(100% + 40px); width: calc(var(--margen) - 14px); text-align: right;
  font: 500 .7rem/1.25 var(--f-mono); letter-spacing: .1em; text-transform: uppercase; color: var(--terracota);
}
@media (max-width: 760px) { .apuntes section::before { position: static; display: block; width: auto; text-align: left; margin-bottom: 4px; } }
.apuntes h2 { font: 800 clamp(1.7rem, 2.8vw, 2.25rem)/1.12 var(--f-tit); margin: 0 0 .5em; letter-spacing: -.01em; }
.apuntes p { margin: 0 0 1em; }
.apuntes .katex-display { margin: 1.1em 0; overflow-x: auto; overflow-y: hidden; padding: 4px 0; }
.apuntes .katex { font-size: 1.12em; }
.apuntes .formula { background: var(--blanco); border: 2px solid var(--pizarra); border-radius: 8px; box-shadow: var(--sombra-p); padding: 4px 20px; margin: 1.4em 0; }
.apuntes .nota { border-left: 2.5px solid var(--terracota); padding: 2px 0 2px 18px; color: var(--madera); font-size: 1rem; margin: 1.2em 0; }
.bloque { position: relative; background: var(--blanco); border: 2px solid var(--pizarra); border-radius: 10px; padding: 20px 22px 8px; margin: 2em 0 1.6em; box-shadow: var(--sombra-p); }
.bloque__tit {
  /* En el flujo (no absoluto): si el título ocupa dos líneas en móvil, empuja el contenido en vez de taparlo */
  position: relative; display: table; margin: -35px 0 9px -6px; padding: 5px 12px; border-radius: 6px; max-width: calc(100% + 12px);
  font: 600 .76rem/1.25 var(--f-mono); letter-spacing: .05em; background: var(--blanco); color: var(--pizarra); border: 2px solid var(--pizarra);
}
.bloque__tit .katex { font-size: 1.1em; }
.bloque.teorema .bloque__tit { background: var(--pizarra); color: var(--papel); }
.bloque.demostracion { border-color: var(--terracota); box-shadow: 4px 4px 0 var(--terracota); padding-bottom: 46px; }
.bloque.demostracion .bloque__tit { background: var(--terracota); color: var(--blanco); border-color: var(--terracota); }
.bloque.demostracion::after { content: '∎'; position: absolute; right: 18px; bottom: 10px; font-size: 1.4rem; color: var(--terracota); }
.bloque.ejemplo .bloque__tit { background: var(--salvia); color: var(--pizarra-prof); }
.bloque.idea { border-color: var(--terracota); box-shadow: none; background: rgba(252, 252, 252, .85); }
.bloque.idea .bloque__tit { color: var(--terracota-osc); border-color: var(--terracota); }
.bloque.historia { background: #FBF6E6; border-color: var(--madera); box-shadow: 4px 4px 0 var(--madera); }
.bloque.historia .bloque__tit { background: #FBF6E6; color: var(--madera); border-color: var(--madera); font-style: italic; }
.tabla { width: 100%; border-collapse: collapse; margin: 1.4em 0; font-size: .98rem; background: var(--blanco); border: 2px solid var(--pizarra); }
.tabla th { font: 600 .78rem/1.3 var(--f-mono); letter-spacing: .02em; text-align: left; padding: 10px 12px; background: var(--pizarra); color: var(--papel); }
.tabla td { padding: 10px 12px; border-top: 1px solid var(--borde); }
.tabla--num td, .tabla--num th { text-align: center; }
.pasos { padding-left: 1.4em; }
.pasos li { margin-bottom: .7em; padding-left: .3em; }
.pasos li::marker { font: 700 1rem var(--f-mono); color: var(--terracota); }
.ejercicios { padding-left: 0; list-style: none; counter-reset: ej; }
.ejercicios > li { counter-increment: ej; position: relative; padding: 16px 18px 12px 62px; margin-bottom: 14px; background: var(--blanco); border: 1.5px solid var(--borde); border-radius: 10px; }
.ejercicios > li::before { content: counter(ej); position: absolute; left: 16px; top: 14px; width: 32px; height: 32px; border-radius: 50%; background: var(--pizarra); color: var(--papel); display: grid; place-items: center; font: 700 .95rem var(--f-mono); }
.ejercicios details { border-top: 1.5px dashed var(--borde); padding-top: 8px; }
.ejercicios summary { cursor: pointer; font: 700 .8rem/1 var(--f-mono); letter-spacing: .08em; text-transform: uppercase; color: var(--terracota-osc); list-style: none; display: inline-flex; gap: .5em; align-items: center; padding: 6px 0; }
.ejercicios summary::-webkit-details-marker { display: none; }
.ejercicios summary::before { content: '+'; display: inline-grid; place-items: center; width: 20px; height: 20px; border: 1.5px solid currentColor; border-radius: 4px; transition: transform .25s; }
.ejercicios details[open] summary::before { transform: rotate(45deg); }
.ejercicios details p { margin: .5em 0; background: linear-gradient(transparent 0, transparent); }

.pasar-nav { display: grid; grid-template-columns: 1fr 1fr; gap: 20px; margin-top: 60px; }
.pasar { text-decoration: none; display: block; padding: 18px 20px; border: 2px solid var(--pizarra); border-radius: 10px; background: var(--blanco); box-shadow: var(--sombra-p); transition: transform .2s var(--ease); }
.pasar:hover { transform: translate(-2px, -2px); }
.pasar--sig { text-align: right; }
.pasar--vacio { border: 0; background: none; box-shadow: none; }
.pasar__etq { display: block; font: 500 .72rem/1 var(--f-mono); color: var(--terracota); letter-spacing: .1em; text-transform: uppercase; margin-bottom: 6px; }
.pasar__tit { font: 700 1.2rem/1.2 var(--f-tit); }
.progreso { position: fixed; top: 0; bottom: 0; left: calc(var(--margen) - 3px); width: 8px; z-index: 40; pointer-events: none; }
.progreso span { display: block; width: 100%; height: 0; background: var(--salvia); border-radius: 0 0 4px 4px; }

/* Laboratorios (labs.js) con la marca Cuaderno */
.lab { --lab-tinta: #1E3D33; --lab-acento: #B5523B; --lab-relleno: rgba(122,157,130,.42); --lab-rejilla: rgba(30,61,51,.08); --lab-tenue: rgba(30,61,51,.5); --lab-fuente: 'JetBrains Mono', monospace;
  background: var(--blanco); border: 2px solid var(--pizarra); border-radius: 12px; box-shadow: var(--sombra); padding: 16px 18px 18px; margin: 2em 0; }
.lab__cabecera { display: flex; gap: 12px; align-items: center; margin-bottom: 12px; flex-wrap: wrap; }
.lab__chip { background: var(--terracota); color: var(--blanco); font: 700 .68rem/1 var(--f-mono); letter-spacing: .12em; text-transform: uppercase; padding: 6px 9px; border-radius: 999px; }
.lab__titulo { font: 700 1.05rem/1.2 var(--f-tit); }
.lab__cuerpo { display: grid; grid-template-columns: minmax(0, 1.5fr) minmax(220px, 1fr); gap: 18px; align-items: start; }
@media (max-width: 720px) { .lab__cuerpo { grid-template-columns: 1fr; } }
.lab__grafico { background-color: var(--papel); background-image: linear-gradient(var(--cuadricula) 1px, transparent 1px), linear-gradient(90deg, var(--cuadricula) 1px, transparent 1px); background-size: 14px 14px; border-radius: 8px; border: 1.5px solid var(--borde); overflow: hidden; min-width: 0; }
.lab__lienzo { display: block; }
.lab__control { display: grid; grid-template-columns: 28px 1fr 46px; align-items: center; gap: 8px; margin-bottom: 8px; }
.lab__control output { font: 600 .85rem var(--f-mono); text-align: right; }
.lab input[type=range] { width: 100%; accent-color: var(--terracota); }
.lab__botones { display: flex; flex-wrap: wrap; gap: 6px; margin: 10px 0; }
.lab__botones button { font: 700 .76rem/1 var(--f-txt); padding: 8px 10px; border-radius: 999px; border: 1.5px solid var(--pizarra); background: var(--blanco); color: var(--pizarra); cursor: pointer; }
.lab__botones button[aria-pressed=true], .lab__botones button:hover { background: var(--pizarra); color: var(--papel); }
.lab__lectura { font-size: .95rem; }
.lab__dato { margin: 6px 0; overflow-x: auto; overflow-y: hidden; }
.lab__dato--grande { font-size: 1.25rem; }
.lab__veredicto { font: 700 .9rem/1.3 var(--f-txt); color: var(--terracota-osc); margin: 8px 0; }
.lab__aviso { font-size: .85rem; color: var(--madera); margin: 8px 0 0; }
.lab__barra { height: 8px; border-radius: 4px; background: var(--papel-osc); overflow: hidden; margin: 8px 0 4px; }
.lab__barra span { display: block; height: 100%; background: var(--terracota); transition: width .3s; }
.lab__fraccion { display: inline-flex; flex-direction: column; align-items: center; gap: 6px; margin: 4px 0 8px; }
.lab__fraccion label { display: flex; gap: 8px; align-items: center; font: italic 700 1.1rem var(--f-tit); }
.lab__fraccion input { width: 110px; font: 700 1.2rem var(--f-mono); text-align: center; padding: 6px; border: 2px solid var(--pizarra); border-radius: 6px; background: var(--papel); color: var(--pizarra); }
.lab__raya { width: 150px; height: 3px; background: var(--pizarra); border-radius: 2px; margin-left: 18px; }
.mesa .lapiz { top: 0; left: 0; margin: -38px 0 0 -7px; }
.prueba li > span:first-child { white-space: nowrap; }
@media (max-width: 900px) {
  .prueba li { flex-direction: column; align-items: flex-start; gap: 2px; margin-bottom: 14px; }
  .prueba li .txt { margin-left: 0; font-size: .78em; }
  .prueba__titulo { margin-bottom: .4em; }
  .mesa .sello { left: auto; right: 0; top: 0; width: 104px; height: 104px; font-size: 1.15rem; }
}

/* =========================================================================
   Páginas generadas: índice de capítulos, shorts, 404 y piezas compartidas
   ========================================================================= */
.vh { position: absolute; width: 1px; height: 1px; overflow: hidden; clip: rect(0 0 0 0); white-space: nowrap; }
.cab nav a[aria-current="page"]:not(.btn) { text-decoration: underline; text-decoration-thickness: 2px; text-underline-offset: 6px; text-decoration-color: var(--terracota); }

/* Rotaciones de las tarjetas, también más allá de la cuarta */
.demo:nth-child(4n+1) { --r: -1.2deg; } .demo:nth-child(4n+2) { --r: .9deg; }
.demo:nth-child(4n+3) { --r: -.6deg; } .demo:nth-child(4n) { --r: 1.1deg; }
.demo h3 a { color: inherit; text-decoration: none; }
.demo h3 a::after { content: ''; position: absolute; inset: 0; z-index: 0; }   /* toda la tarjeta lleva a los apuntes */
.demo__mini, .demo__acc { position: relative; z-index: 1; }
.demo[hidden] { display: none; }

.ver-todo { margin: clamp(36px, 4vw, 56px) 0 0; text-align: center; }
.enlace-flecha { font: 600 1rem/1.3 var(--f-txt); color: var(--terracota-osc); text-decoration: none; border-bottom: 2px solid var(--subrayador); }
.enlace-flecha:hover { border-color: var(--terracota); }

/* Cabecera de las páginas interiores */
.indice { padding-top: clamp(130px, 14vw, 170px); }
.indice__tit { font: 800 clamp(2.6rem, 6vw, 4.6rem)/1 var(--f-tit); letter-spacing: -.02em; margin: .25em 0 .35em; }

/* Filtros del índice */
.filtros { display: flex; flex-wrap: wrap; gap: 14px 24px; align-items: center; justify-content: space-between; margin-bottom: clamp(36px, 4vw, 52px); }
.filtros__temas { display: flex; flex-wrap: wrap; gap: 10px; }
.filtro { font: 600 .9rem/1 var(--f-txt); color: var(--pizarra); background: var(--blanco); border: 2px solid var(--pizarra); border-radius: 999px; padding: .6em 1.05em; cursor: pointer; transition: background .2s, color .2s, transform .2s var(--ease); }
.filtro:hover { transform: translateY(-2px); }
.filtro[aria-pressed="true"] { background: var(--pizarra); color: var(--papel); box-shadow: 3px 3px 0 var(--terracota); }
.filtros__buscar input { font: 500 1rem/1 var(--f-txt); color: var(--pizarra); width: min(360px, 100%); padding: .75em 1em; border: 2px solid var(--pizarra); border-radius: 10px; background: var(--blanco); box-shadow: var(--sombra-p); }
.filtros__buscar input:focus { outline: 3px solid var(--subrayador); outline-offset: 2px; }
@media (max-width: 680px) { .filtros__buscar, .filtros__buscar input { width: 100%; } }
.indice__vacio { font: italic 600 1.2rem/1.4 var(--f-tit); color: var(--madera); text-align: center; padding: 40px 0; }

/* Rejilla de shorts (página /shorts/ y apuntes) */
.rejilla-shorts { display: grid; grid-template-columns: repeat(auto-fill, minmax(min(210px, 100%), 1fr)); gap: clamp(28px, 3vw, 44px); align-items: start; }
.rejilla-shorts__item { display: flex; flex-direction: column; gap: 18px; }
.rejilla-shorts__item .enlace-flecha { align-self: flex-start; font-size: .9rem; }
.rejilla-shorts .short:nth-child(3n+1), .rejilla-shorts__item:nth-child(3n+1) .short { --r: 1.8deg; }
.rejilla-shorts .short:nth-child(3n+2), .rejilla-shorts__item:nth-child(3n+2) .short { --r: -2.2deg; }
.rejilla-shorts .short:nth-child(3n), .rejilla-shorts__item:nth-child(3n) .short { --r: .8deg; }
.ap-shorts .rejilla-shorts { grid-template-columns: repeat(auto-fill, minmax(min(190px, 100%), 230px)); }
.short.rv.vis { transform: rotate(var(--r, 2deg)); }

/* Móvil: «Capítulos» sigue visible en la cabecera; el botón de suscripción se queda en icono */
@media (max-width: 860px) { .cab nav a[href="/capitulos/"] { display: inline; font-size: .95rem; } }
@media (max-width: 440px) { .cab__sus { display: none; } .cab .btn--yt { padding: .62em .8em; } }

/* Fórmulas largas en pantallas estrechas: se desplazan dentro de su línea en vez de ensanchar la página */
.ap-cuerpo > * { min-width: 0; }
.apuntes .katex-display { overflow-x: auto; overflow-y: hidden; padding: 2px 0 6px; }
.apuntes .tabla { display: block; overflow-x: auto; }
@media (min-width: 761px) { .apuntes .tabla { display: table; } }