:root{
  --primary:#1967d2;
  --primary-dark:#104a9b;
  --primary-soft:#eaf2ff;
  --bg:#eef3f8;
  --surface:#fff;
  --surface-soft:#f8fbff;
  --line:#d7e0ec;
  --text:#172033;
  --muted:#627086;
  --ok:#087f5b;
  --ok-bg:#eefbf6;
  --warn:#956700;
  --warn-bg:#fff8df;
  --danger:#aa281f;
  --danger-bg:#fff2f1;
  --violet:#6548c7;
  --shadow:0 8px 28px rgba(15,23,42,.08);
}

*{box-sizing:border-box;min-width:0}
html{scroll-behavior:smooth;overflow-x:hidden}
body{margin:0;min-height:100vh;font-family:"Segoe UI",Arial,sans-serif;background:var(--bg);color:var(--text);line-height:1.62;overflow-x:hidden}
body.drawer-open{overflow:hidden}
button,input{font:inherit}
button{touch-action:manipulation}
a{color:var(--primary-dark)}
img,svg{max-width:100%;height:auto}

.site-header{
  height:52px;background:var(--primary);color:#fff;display:flex;align-items:center;
  justify-content:space-between;gap:14px;padding:0 16px;box-shadow:0 2px 8px #0002;
  position:sticky;top:0;z-index:90
}
.brand-link{display:flex;align-items:center;gap:8px;color:#fff;text-decoration:none;font-weight:800}
.brand-mark{display:grid;place-items:center;width:30px;height:30px;border:1px solid #ffffff80;border-radius:8px;background:#ffffff18;font-size:12px}
.site-header>strong{font-size:14px;white-space:nowrap;overflow:hidden;text-overflow:ellipsis}

.course-view{min-height:calc(100vh - 52px)}
.course-toolbar{
  min-height:50px;background:rgba(255,255,255,.96);backdrop-filter:blur(10px);
  border-bottom:1px solid var(--line);display:flex;align-items:center;gap:8px;padding:7px 14px;
  position:sticky;top:52px;z-index:80
}
.pill-button,.module-pill{border-radius:999px;padding:7px 12px;font-size:12.5px;font-weight:800;white-space:nowrap}
.pill-button{border:1px solid #bdd2ef;background:#fff;color:var(--primary-dark);cursor:pointer;text-decoration:none}
.pill-button:hover{background:var(--primary-soft)}
.module-pill{background:var(--primary-soft);color:var(--primary-dark);border:1px solid #bdd2ef}
.menu-toggle{margin-left:auto;background:var(--primary);color:#fff;border-color:var(--primary)}
.menu-toggle:hover{background:var(--primary-dark)}

.lesson-menu{
  position:fixed;top:102px;left:0;bottom:0;width:min(330px,88vw);padding:14px 12px 24px;
  background:#fff;border-right:1px solid var(--line);box-shadow:12px 0 32px rgba(15,23,42,.16);
  overflow-y:auto;z-index:100;transform:translateX(-105%);transition:transform .2s ease
}
.lesson-menu.open{transform:translateX(0)}
.menu-backdrop{position:fixed;inset:102px 0 0;background:rgba(15,23,42,.34);z-index:95}
.drawer-heading{padding:4px 8px 13px;border-bottom:1px solid var(--line);margin-bottom:6px}
.drawer-heading strong{display:block;color:var(--primary-dark);font-size:16px}
.drawer-heading span{display:block;color:var(--muted);font-size:12px;margin-top:2px}
.menu-group-title{font-size:10px;text-transform:uppercase;letter-spacing:.08em;color:var(--muted);font-weight:900;padding:12px 8px 5px}
.menu-item{
  width:100%;display:grid;grid-template-columns:34px 1fr;align-items:center;gap:8px;border:0;
  background:transparent;text-align:left;color:#172033;font-size:13px;font-weight:750;line-height:1.2;
  padding:9px 8px;border-radius:9px;margin:2px 0;cursor:pointer
}
.menu-number{display:grid;place-items:center;width:31px;height:27px;border-radius:7px;background:#f0f4f9;color:var(--muted);font-size:11px;font-weight:900}
.menu-item:hover,.menu-item.active{background:var(--primary-soft);color:var(--primary-dark)}
.menu-item.active .menu-number{background:var(--primary);color:#fff}

.content-area{width:min(1060px,100%);margin:0 auto;padding:20px clamp(12px,2.5vw,26px) 48px}
.lesson-heading{display:grid;grid-template-columns:minmax(0,1.45fr) minmax(250px,.8fr);gap:20px;align-items:end;margin:2px 0 14px}
.unit-name{font-size:10.5px;font-weight:900;color:var(--primary);text-transform:uppercase;letter-spacing:.08em}
.technical-title{font-size:12px;font-weight:800;color:var(--muted);margin-top:2px;overflow-wrap:anywhere}
.lesson-heading h1{font-size:clamp(25px,3vw,37px);line-height:1.08;color:var(--primary-dark);margin:5px 0 0;letter-spacing:-.02em}
.lesson-objective{font-size:13px;line-height:1.45;margin:0;padding:12px 14px;background:#fff;border:1px solid var(--line);border-radius:11px;color:#42536a}

.lesson-content{
  background:var(--surface);border:1px solid var(--line);border-radius:16px;
  padding:clamp(17px,2.7vw,30px);box-shadow:var(--shadow);overflow:hidden
}
.lesson-content>*:first-child{margin-top:0}
.lesson-content h2{font-size:clamp(22px,2.6vw,31px);line-height:1.2;color:var(--primary-dark);margin:5px 0 10px}
.lesson-content h3{font-size:clamp(19px,2vw,23px);line-height:1.25;color:var(--primary-dark);margin:30px 0 9px}
.lesson-content p{margin:8px 0}
.lesson-content ul,.lesson-content ol{margin:8px 0 12px 22px;padding:0}
.lesson-content li{margin:5px 0}
.lesson-content strong{font-weight:800}
.eyebrow{display:block;color:var(--primary);font-size:11px;font-weight:900;text-transform:uppercase;letter-spacing:.08em;margin-bottom:6px}

.hero-box,.definition-box,.example-box,.note-box,.ok-box,.danger-box,.bridge-box,.mbb-pause-question,.essence,.checkpoint{
  border-radius:12px;padding:16px 17px;margin:16px 0
}
.hero-box{background:linear-gradient(135deg,#eaf3ff 0%,#f8fbff 60%,#fff 100%);border:1px solid #bdd4f4}
.story-opening p{font-size:16px;line-height:1.65}
.definition-box,.example-box{background:var(--surface-soft);border:1px solid var(--line)}
.definition-box{border-left:4px solid #8db6ee}
.definition-box.featured{border:2px solid #9fc2f2;background:#f5f9ff}
.definition-box.compact,.note-box.compact,.danger-box.compact,.example-box.compact,.ok-box.compact{padding:12px 14px;margin:11px 0}
.term{display:block;color:var(--primary-dark);font-weight:900;font-size:16px;margin-bottom:4px}
.note-box{background:var(--warn-bg);border-left:5px solid #d59b00}
.ok-box{background:var(--ok-bg);border-left:5px solid var(--ok)}
.danger-box{background:var(--danger-bg);border-left:5px solid var(--danger)}
.bridge-box{background:#f5f2ff;border:1px solid #ded5ff;border-left:5px solid var(--violet)}
.mbb-pause-question{background:#eef6ff;border:1px solid #bdd4f4;border-left:5px solid var(--primary)}
.essence{border:2px solid #b9d3f6;background:#f8fbff}
.essence>strong{display:block;color:var(--primary-dark);font-size:17px;margin-bottom:4px}

.historical-media{
  width:min(100%,560px);margin:20px auto;border:1px solid var(--line);border-radius:13px;
  background:#fff;padding:9px;box-shadow:0 4px 16px rgba(15,23,42,.05)
}
.historical-media.wide{width:min(100%,690px)}
.historical-media.portrait{width:min(100%,320px)}
.historical-media img{display:block;width:100%;max-height:390px;object-fit:contain;border-radius:8px;background:#f5f7fa}
.historical-media.portrait img{max-height:420px}
.historical-media figcaption{font-size:12.2px;line-height:1.45;color:#4d5d73;padding:8px 4px 2px}
.historical-media figcaption strong{color:var(--text)}
.credit{display:block;margin-top:4px;color:var(--muted);font-size:10.5px}
.media-text{display:grid;grid-template-columns:minmax(230px,.82fr) minmax(0,1.18fr);gap:22px;align-items:center;margin:18px 0}
.media-text.reverse{grid-template-columns:minmax(0,1.15fr) minmax(220px,.72fr)}
.media-text.reverse .historical-media{order:2}
.media-text .historical-media{margin:0}

.two-col,.comparison-grid,.bit-combinations{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:12px;margin:15px 0}
.comparison-grid.three{grid-template-columns:repeat(3,minmax(0,1fr))}
.comparison-grid.four{grid-template-columns:repeat(4,minmax(0,1fr))}
.comparison-grid article,.bit-combinations>div{
  background:#fff;border:1px solid var(--line);border-radius:11px;padding:14px
}
.comparison-grid article strong,.bit-combinations strong{display:block;color:var(--primary-dark);margin-bottom:4px}
.comparison-grid article p{font-size:13px;line-height:1.5;color:#475871}

.concept-flow,.system-flow,.representation-flow{
  display:grid;grid-template-columns:1fr auto 1fr auto 1fr;gap:8px;align-items:center;margin:18px 0
}
.concept-flow>div,.flow-node,.representation-flow>div{
  background:var(--primary-soft);border:1px solid #bdd4f4;border-radius:10px;padding:12px;text-align:center
}
.concept-flow strong,.flow-node strong,.representation-flow strong{display:block;color:var(--primary-dark)}
.concept-flow span:not(.flow-arrow),.flow-node span{display:block;color:var(--muted);font-size:11px;margin-top:2px}
.flow-arrow{display:grid;place-items:center;color:var(--primary);font-size:21px;font-weight:900}
.system-flow{grid-template-columns:1fr auto 1.2fr auto 1fr auto 1fr}
.system-flow .processor{background:#f2f7ff}
.representation-flow{grid-template-columns:1fr auto 1.25fr auto 1fr auto .65fr}

.fact-strip{display:grid;grid-template-columns:repeat(4,minmax(0,1fr));gap:9px;margin:15px 0}
.fact-strip>div{background:#f8fbff;border:1px solid var(--line);border-radius:10px;padding:12px;text-align:center}
.fact-strip strong{display:block;color:var(--primary-dark);font-size:17px}
.fact-strip span{display:block;color:var(--muted);font-size:11px;margin-top:2px}

.table-wrap{width:100%;overflow-x:auto;margin:14px 0;border:1px solid var(--line);border-radius:11px}
table{width:100%;border-collapse:collapse;min-width:560px;background:#fff}
th,td{padding:11px 12px;border-bottom:1px solid var(--line);text-align:left;vertical-align:top}
th{background:#f3f7fc;color:var(--primary-dark);font-size:12px}
td{font-size:13px}
tbody tr:last-child td{border-bottom:0}

.checkpoint{background:#f8fbff;border:1px solid #bdd4f4;border-top:4px solid var(--primary);margin-top:26px}
.compact-check{padding:15px}
.quiz-item{border:1px solid var(--line);border-radius:11px;padding:14px;margin:10px 0;background:#fff;transition:.15s ease}
.quiz-item>p{font-weight:800;margin:0 0 8px;line-height:1.48}
.quiz-item label{display:block;padding:7px 9px;margin:4px 0;border-radius:8px;cursor:pointer;font-size:13px}
.quiz-item label:hover{background:#f6f9fd}
.quiz-item input{margin-right:7px}
.quiz-item.is-correct{border-color:#91d2bd;background:#f7fdfb}
.quiz-item.is-wrong{border-color:#efb3ad;background:#fffafa}
.quiz-result{margin-top:12px}
.feedback-list{margin:8px 0 0 20px!important}
.feedback-list li{margin:6px 0!important}

.action-button{
  border:1px solid #b9d3f6;background:#fff;color:var(--primary-dark);font-weight:800;
  border-radius:9px;padding:10px 13px;cursor:pointer
}
.action-button.primary{background:var(--primary);color:#fff;border-color:var(--primary)}
.action-button:hover{filter:brightness(.98)}
.lesson-navigation{display:flex;gap:9px;flex-wrap:wrap;justify-content:space-between;border-top:1px solid var(--line);padding-top:18px;margin-top:28px}

.binary-states,.unit-contrast{display:grid;grid-template-columns:repeat(2,minmax(0,180px));justify-content:center;gap:14px;margin:16px 0}
.binary-states>div,.unit-contrast>div{border:1px solid #bdd4f4;background:#f6faff;border-radius:12px;text-align:center;padding:14px}
.binary-states strong,.unit-contrast strong{display:block;color:var(--primary-dark);font-size:28px;line-height:1}
.binary-states span,.unit-contrast span{display:block;color:var(--muted);font-size:12px;margin-top:5px}
.bit-combinations{grid-template-columns:repeat(4,minmax(0,1fr))}
.bit-combinations span,.bit-combinations code{display:block;font-size:11px;color:var(--muted);margin-top:4px;overflow-wrap:anywhere}
.code-focus{text-align:center;margin:15px 0}
.code-focus code{display:inline-block;padding:10px 14px;background:#111827;color:#f8fafc;border-radius:9px;font-size:clamp(16px,3vw,23px);letter-spacing:.06em}
.encoding-demo{display:flex;align-items:center;justify-content:center;gap:8px;flex-wrap:wrap;background:#f8fbff;border:1px solid var(--line);border-radius:11px;padding:14px;margin:14px 0}
.encoding-demo span{font-size:11px;color:var(--muted);text-transform:uppercase;font-weight:800}
.encoding-demo strong,.encoding-demo code{font-size:18px;color:var(--primary-dark)}
.unit-contrast{grid-template-columns:repeat(2,minmax(0,220px))}

.sources-box{margin:24px 0 4px;border-top:1px solid var(--line);padding-top:12px;color:var(--muted);font-size:12px}
.sources-box summary{cursor:pointer;color:var(--primary-dark);font-weight:800}
.sources-box ul{margin-top:8px}
.sources-box a{overflow-wrap:anywhere}

@media(max-width:900px){
  .lesson-heading{grid-template-columns:1fr;gap:8px;align-items:start}
  .lesson-objective{max-width:760px}
  .comparison-grid.four{grid-template-columns:repeat(2,minmax(0,1fr))}
  .comparison-grid.three{grid-template-columns:repeat(2,minmax(0,1fr))}
  .bit-combinations{grid-template-columns:repeat(2,minmax(0,1fr))}
  .system-flow{grid-template-columns:1fr}
  .system-flow .flow-arrow{transform:rotate(90deg)}
  .representation-flow{grid-template-columns:1fr}
  .representation-flow .flow-arrow{transform:rotate(90deg)}
}

@media(max-width:700px){
  .site-header{padding:0 11px}
  .site-header>strong{max-width:44vw}
  .course-toolbar{padding:6px 9px;gap:6px}
  .module-pill{display:none}
  .content-area{padding:14px 8px 34px}
  .lesson-heading{padding:0 4px}
  .lesson-heading h1{font-size:26px}
  .lesson-objective{font-size:12.5px}
  .lesson-content{border-radius:12px;padding:15px 12px}
  .lesson-content h3{margin-top:25px}
  .story-opening p{font-size:15px}
  .media-text,.media-text.reverse{grid-template-columns:1fr;gap:8px}
  .media-text.reverse .historical-media{order:0}
  .historical-media,.historical-media.wide,.historical-media.portrait{width:min(100%,540px);margin:14px auto}
  .historical-media img,.historical-media.portrait img{max-height:none}
  .two-col,.comparison-grid,.comparison-grid.three,.comparison-grid.four{grid-template-columns:1fr}
  .concept-flow{grid-template-columns:1fr}
  .concept-flow .flow-arrow{transform:rotate(90deg)}
  .fact-strip{grid-template-columns:repeat(2,minmax(0,1fr))}
  .binary-states,.unit-contrast{grid-template-columns:repeat(2,minmax(0,1fr))}
  .bit-combinations{grid-template-columns:1fr 1fr}
  .lesson-navigation{display:grid;grid-template-columns:1fr}
  .lesson-navigation .action-button{width:100%;text-align:center}
  .quiz-item{padding:12px 10px}
  .quiz-item label{padding:8px 6px}
}

@media(max-width:390px){
  .back-link{padding:7px 9px}
  .menu-toggle{padding:7px 9px}
  .site-header .brand-link>span:last-child{display:none}
  .site-header>strong{max-width:62vw}
  .fact-strip,.bit-combinations{grid-template-columns:1fr}
  .binary-states,.unit-contrast{gap:8px}
}