/* GCSE Computer Science Explained v2: paper and ink, squared paper, bits. Palette and type follow /workspace/gcse/house-style.md */
@font-face{font-family:"Instrument Serif";src:url(fonts/InstrumentSerif-Regular.woff2) format("woff2");font-weight:400;font-display:swap}
@font-face{font-family:"IBM Plex Sans";src:url(fonts/IBMPlexSans-Regular.woff2) format("woff2");font-weight:400;font-display:swap}
@font-face{font-family:"IBM Plex Sans";src:url(fonts/IBMPlexSans-Medium.woff2) format("woff2");font-weight:500;font-display:swap}
@font-face{font-family:"IBM Plex Sans Condensed";src:url(fonts/IBMPlexSansCondensed-Medium.woff2) format("woff2");font-weight:500;font-display:swap}
@font-face{font-family:"IBM Plex Mono";src:url(fonts/IBMPlexMono-Medium.woff2) format("woff2");font-weight:500;font-display:swap}
:root{--paper:#F2EDE4;--paper2:#EAE3D6;--ink:#1E2328;--teal:#2F7A6B;--teal-text:#246659;--red:#C8462B;--red-text:#AC3820;--muted:#6A645A;--rule:#D9D1C3;
--serif:"Instrument Serif",Georgia,"Times New Roman",serif;--sans:"IBM Plex Sans",-apple-system,"Segoe UI",Roboto,Arial,sans-serif;
--cond:"IBM Plex Sans Condensed","Arial Narrow",sans-serif;--mono:"IBM Plex Mono",ui-monospace,Menlo,Consolas,monospace}
*{box-sizing:border-box}html{-webkit-text-size-adjust:100%;scroll-behavior:smooth}
body{margin:0;color:var(--ink);font:400 17px/1.65 var(--sans);background-color:var(--paper);
background-image:linear-gradient(rgba(30,35,40,.045) 1px,transparent 1px),linear-gradient(90deg,rgba(30,35,40,.045) 1px,transparent 1px);background-size:24px 24px}
a{color:var(--teal-text);text-underline-offset:3px;text-decoration-thickness:1px}a:hover{color:var(--ink)}
code{font-family:var(--mono);font-weight:500;font-size:.92em}
.wrap{max-width:1040px;margin:0 auto;padding:0 24px}
.skip{position:absolute;left:-999px;top:8px;background:var(--ink);color:var(--paper);padding:8px 12px;z-index:10}.skip:focus{left:8px}
:focus-visible{outline:2px solid var(--teal);outline-offset:3px}
/* reading progress line (house style 1.7), progressive enhancement */
.progress{position:fixed;left:0;top:0;height:3px;width:100%;background:var(--teal);transform-origin:0 50%;transform:scaleX(0);z-index:20;display:none}
@supports (animation-timeline:scroll()){.progress{display:block;animation:grow linear both;animation-timeline:scroll(root)}}
@keyframes grow{to{transform:scaleX(1)}}
/* header strip + index-card tabs */
.strip{background:var(--paper);border-bottom:1px solid var(--ink)}
.strip .wrap:first-child{display:flex;align-items:center;justify-content:space-between;gap:16px;min-height:60px;border-bottom:1px solid var(--rule)}
.brand{display:flex;align-items:center;gap:12px;text-decoration:none;color:var(--ink)}
.brand svg{width:30px;height:30px;flex:none}
.brand span{font-family:var(--cond);font-weight:500;text-transform:uppercase;letter-spacing:.06em;font-size:.95rem}
.brand b{font-weight:500;color:var(--teal-text)}
.spec{font-family:var(--mono);font-size:.78rem;color:var(--muted);white-space:nowrap}
.tabs{display:flex;gap:6px;overflow-x:auto;padding-top:10px;scrollbar-width:none}
.tabs a{font-family:var(--cond);font-weight:500;font-size:.86rem;letter-spacing:.06em;text-transform:uppercase;text-decoration:none;color:var(--muted);
border:1px solid var(--rule);border-bottom:0;border-radius:6px 6px 0 0;padding:6px 14px 5px;background:var(--paper2);white-space:nowrap}
.tabs a:hover{color:var(--ink);border-color:var(--ink)}
.tabs a[aria-current]{background:var(--ink);color:var(--paper);border-color:var(--ink)}
/* type */
h1,h2,h3{font-family:var(--serif);font-weight:400;line-height:1.1;color:var(--ink)}
h1{font-size:clamp(2.4rem,5.4vw,4rem);margin:0 0 20px;letter-spacing:-.005em}
h1 em,h2 em{font-style:normal;color:var(--teal-text);background:linear-gradient(transparent 82%,rgba(47,122,107,.28) 82%)}
h2{font-size:clamp(1.9rem,3.6vw,2.5rem);margin:0 0 12px}
.eyebrow{font-family:var(--cond);font-weight:500;font-size:.85rem;letter-spacing:.12em;text-transform:uppercase;color:var(--muted);margin:0 0 14px}
.kicker{font-family:var(--mono);font-size:.8rem;color:var(--muted);margin:0 0 6px;text-transform:uppercase;letter-spacing:.08em}
.kicker span{display:inline-block;background:var(--ink);color:var(--paper);border-radius:3px;padding:1px 7px;margin-right:8px;letter-spacing:0}
.lede{font-size:1.12rem;color:#3a3f45;max-width:32em;margin:0}
.measure{max-width:40em;color:#3a3f45;margin:0}
.muted{color:var(--muted)}
/* hero */
.hero{padding:64px 0 60px;border-bottom:1px solid var(--rule)}
.hero .wrap{display:grid;grid-template-columns:minmax(0,1.25fr) minmax(0,1fr);gap:48px;align-items:center}
.facts{list-style:none;padding:0;margin:26px 0 0;display:grid;gap:8px}
.facts li{font-size:.98rem;padding-left:22px;position:relative;color:#3a3f45}
.facts li::before{content:"";position:absolute;left:0;top:.5em;width:10px;height:10px;background:var(--teal);border-radius:2px}
.facts b{font-weight:500;color:var(--ink)}
.hero-art{display:grid;gap:22px}
/* terminal card */
.term{margin:0;background:var(--ink);color:var(--paper);border-radius:8px;font-family:var(--mono);font-weight:500;font-size:.95rem;line-height:1.6;overflow:hidden;box-shadow:6px 6px 0 var(--teal)}
.term .bar{display:flex;align-items:center;gap:6px;padding:8px 12px;background:#2a3036;font-size:.72rem;color:#b9b2a6}
.term .bar i{width:9px;height:9px;border-radius:50%;background:#4a525a}.term .bar span{margin-left:8px}
.term code{display:block;padding:14px 18px 16px;font-size:inherit;white-space:pre}
.term .p{color:#8FC7B9}.term .o{color:#E9C98E}
.term .cur{display:inline-block;width:.6em;height:1.1em;vertical-align:-.2em;background:var(--paper);opacity:.8}
/* the register */
.register{margin:0;font-family:var(--mono);font-weight:500}
.register .pv,.register .bits{display:grid;grid-template-columns:repeat(8,1fr);gap:6px}
.register .pv span{text-align:center;font-size:.72rem;color:var(--muted);padding-bottom:6px}
.register .bits span{aspect-ratio:3/4;display:flex;align-items:center;justify-content:center;border:2px solid var(--ink);border-radius:4px;font-size:1.3rem;background:var(--paper2)}
.register .bits span.on{background:var(--ink);color:var(--paper)}
.register figcaption{margin:12px 0 0;font-size:.8rem;color:var(--muted)}
.register figcaption b{font-weight:500;color:var(--teal-text)}
/* sections */
section.block{padding:56px 0;border-bottom:1px solid var(--rule)}
/* featured video */
.vgrid{display:grid;grid-template-columns:minmax(0,1.6fr) minmax(0,1fr);gap:32px;align-items:center;margin-top:24px}
.player{position:relative;aspect-ratio:16/9;border:2px solid var(--ink);border-radius:8px;overflow:hidden;background:var(--paper2);box-shadow:6px 6px 0 var(--ink)}
.player iframe{position:absolute;inset:0;width:100%;height:100%;border:0}
.player video{position:absolute;inset:0;width:100%;height:100%;background:var(--paper);display:block}
.player .play{position:absolute;inset:0;display:block;color:inherit;text-decoration:none}
.poster{position:absolute;inset:0;display:flex;flex-direction:column;justify-content:center;align-items:center;gap:10px;text-align:center;padding:20px;
background-color:var(--paper);background-image:linear-gradient(rgba(30,35,40,.06) 1px,transparent 1px),linear-gradient(90deg,rgba(30,35,40,.06) 1px,transparent 1px);background-size:20px 20px}
.poster .pt{font-family:var(--serif);font-size:clamp(1.8rem,4.4vw,3rem);line-height:1}
.poster .pbits{font-family:var(--mono);font-size:clamp(.9rem,2vw,1.2rem);letter-spacing:.1em;color:var(--teal-text)}
.poster .soon{font-family:var(--cond);font-weight:500;font-size:.9rem;letter-spacing:.08em;text-transform:uppercase;color:var(--muted);border:1px dashed var(--muted);border-radius:4px;padding:4px 10px;margin-top:6px}
.player .btn{position:absolute;left:50%;top:50%;width:76px;height:76px;margin:-38px 0 0 -38px;border-radius:50%;background:var(--ink);display:flex;align-items:center;justify-content:center;transition:background .2s}
.player .btn svg{width:34px;height:34px;fill:var(--paper);margin-left:4px}
.player .play:hover .btn,.player .play:focus-visible .btn{background:var(--teal)}
.player .play .poster{justify-content:flex-end;padding-bottom:22px}
.vside h3{font-size:2rem;margin:0 0 6px}
.vside p{margin:0 0 12px;color:#3a3f45}
.vspec{font-family:var(--mono);font-size:.78rem;color:var(--muted)!important;white-space:pre-wrap}
.vnote{font-size:.8rem;color:var(--muted);margin:10px 0 0}
#video>.wrap>p:last-child{margin:28px 0 0}
.btnlink{display:inline-block;font-family:var(--cond);font-weight:500;letter-spacing:.06em;text-transform:uppercase;background:var(--ink);color:var(--paper);text-decoration:none;padding:10px 16px;border-radius:4px}
.btnlink:hover{background:var(--teal);color:var(--paper)}
/* topics */
.topics{list-style:none;padding:0;margin:28px 0 0;display:grid;grid-template-columns:repeat(auto-fill,minmax(290px,1fr));gap:18px}
.topic{background:var(--paper);border:2px solid var(--ink);border-radius:6px;padding:18px 20px 20px;position:relative;display:flex;flex-direction:column}
.topic .n{position:absolute;top:-2px;right:16px;background:var(--ink);color:var(--paper);font-family:var(--mono);font-size:.75rem;padding:2px 8px;border-radius:0 0 4px 4px}
.topic .glyph{align-self:flex-start;background:var(--paper2);border:1px solid var(--rule);border-left:3px solid var(--teal);border-radius:3px;padding:3px 9px;font-size:.85rem;color:var(--ink)}
.topic h3{font-size:1.6rem;margin:14px 0 6px}
.topic p{margin:0 0 14px;color:#3a3f45;font-size:.96rem;flex:1}
.topic .status{font-family:var(--cond);font-weight:500;font-size:.8rem;letter-spacing:.1em;text-transform:uppercase;color:var(--muted)}
.topic:first-child .status{color:var(--teal-text)}
.topic .watch{font-family:var(--cond);font-weight:500;font-size:.85rem;letter-spacing:.08em;text-transform:uppercase}
/* quick check sticky note */
.check{background:transparent}
.note{max-width:560px;margin:0 auto;background:var(--paper2);border-radius:4px;padding:26px 28px 22px 84px;position:relative;box-shadow:0 2px 0 var(--rule),4px 8px 18px rgba(30,35,40,.08);transform:rotate(-1deg)}
.note .qn{position:absolute;left:24px;top:24px;width:42px;height:42px;border:2px solid var(--ink);border-radius:50%;display:flex;align-items:center;justify-content:center;font-family:var(--mono);font-size:.85rem}
.note .eyebrow{margin-bottom:4px}
.note .q{font-family:var(--serif);font-size:1.8rem;line-height:1.2;margin:0 0 12px}
.note .q code{font-size:.8em;background:var(--ink);color:var(--paper);padding:1px 8px;border-radius:3px;letter-spacing:.06em}
.note summary{cursor:pointer;font-family:var(--cond);font-weight:500;letter-spacing:.08em;text-transform:uppercase;font-size:.85rem;color:var(--teal-text)}
.note details p{margin:10px 0 0}.note details b{color:var(--teal-text);font-weight:500}
/* downloads */
.files{list-style:none;padding:0;margin:26px 0 0;border:2px solid var(--ink);border-radius:6px;background:var(--paper);max-width:720px}
.files li{display:grid;grid-template-columns:minmax(0,1.5fr) minmax(0,1fr) auto;gap:12px;align-items:center;padding:12px 16px;border-top:1px solid var(--rule)}
.files li:first-child{border-top:0}
.files code{font-size:.85rem;overflow-wrap:anywhere}
.files li span{font-size:.92rem;color:#3a3f45}
.files .tag{font-family:var(--cond);font-weight:500;font-size:.75rem!important;letter-spacing:.1em;text-transform:uppercase;color:var(--muted)!important;border:1px dashed var(--muted);border-radius:3px;padding:2px 8px}
/* prose */
.prose>*{max-width:42rem}.prose h1{font-size:clamp(2.2rem,4.5vw,3.2rem)}.prose h2{font-size:1.6rem;margin:36px 0 8px}.prose p{color:#3a3f45}
.prose{background:var(--paper)}
/* footer */
footer.site{padding:28px 0 48px;color:var(--muted);font-size:.82rem;line-height:1.6;background:var(--paper)}
footer.site .wrap{display:flex;flex-wrap:wrap;justify-content:space-between;gap:12px 32px}footer.site .wrap>span:nth-child(2){max-width:46em}
footer.site .bytes{flex-basis:100%;margin:0;font-family:var(--mono);color:var(--rule);font-size:.9rem;letter-spacing:.12em}
footer.site a{color:var(--muted)}
@media (max-width:820px){
.hero .wrap,.vgrid{grid-template-columns:1fr;gap:32px}.hero{padding:44px 0 44px}.hero-art{max-width:420px}
.spec{display:none}.note{padding-left:28px;padding-top:76px;transform:none}
.files li{grid-template-columns:1fr auto}.files li span:not(.tag){grid-column:1;grid-row:2;font-size:.85rem}.files .tag{grid-row:1/3;grid-column:2}}
@media (prefers-reduced-motion:reduce){html{scroll-behavior:auto}.progress{display:none!important}.player .btn{transition:none}}