/* ============ RESET & TOKENS ============ */
*,*::before,*::after{box-sizing:border-box;margin:0;padding:0}
html{scroll-behavior:smooth}

:root{
  --bg: #f5f1e8;
  --card: #ffffff;
  --card-soft: #faf6ec;
  --ink: #1a1f2e;
  --ink-soft: #5a6275;
  --ink-faint: #b8bccb;
  --line: #d9d2c0;
  --accent: #c0392b;
  --accent-soft: #e8d5d2;
  --accent-deep: #8b2920;
  --good: #2d6a4f;
  --good-soft: #d8e9df;
  --bad: #c0392b;
  --warn: #b8732e;
  --warn-soft: #f4e3cf;
  --shadow: 0 1px 0 rgba(26,31,46,0.04), 0 8px 24px rgba(26,31,46,0.06);
  --radius: 12px;
}

body{
  font-family:'Outfit',system-ui,sans-serif;
  background:var(--bg);
  color:var(--ink);
  line-height:1.55;
  background-image:
    radial-gradient(circle at 10% 0%, rgba(192,57,43,0.04) 0%, transparent 40%),
    radial-gradient(circle at 90% 100%, rgba(45,106,79,0.04) 0%, transparent 40%);
  min-height:100vh;
}

/* ============ TOPBAR ============ */
.topbar{
  display:flex;align-items:center;justify-content:space-between;
  gap:24px;flex-wrap:wrap;
  padding:20px 32px;
  background:var(--card);
  border-bottom:1px solid var(--line);
  position:sticky;top:0;z-index:50;
}
.brand{display:flex;align-items:center;gap:14px}
.brand-mark{
  font-family:'JetBrains Mono',monospace;
  font-size:28px;font-weight:600;
  color:var(--accent);
  background:var(--accent-soft);
  padding:4px 12px;border-radius:8px;
  letter-spacing:-2px;
}
.brand h1{font-family:'Fraunces',serif;font-size:22px;font-weight:800;letter-spacing:-0.02em}
.brand-sub{font-size:12px;color:var(--ink-soft);text-transform:uppercase;letter-spacing:0.12em;font-weight:500}

.progress-wrap{display:flex;align-items:center;gap:14px}
.progress-label{font-size:12px;color:var(--ink-soft);font-weight:500;min-width:110px;text-align:right}
.progress-bar{width:200px;height:6px;background:var(--line);border-radius:3px;overflow:hidden}
.progress-fill{height:100%;background:linear-gradient(90deg,var(--accent),#e74c3c);width:0;transition:width 0.4s ease}
.reset-btn{
  background:transparent;border:1px solid var(--line);color:var(--ink-soft);
  padding:6px 14px;border-radius:20px;cursor:pointer;font-size:12px;font-weight:500;
  transition:all 0.2s;
}
.reset-btn:hover{background:var(--ink);color:var(--bg);border-color:var(--ink)}

/* ============ TOPIC NAV ============ */
.topic-nav{
  display:flex;gap:6px;flex-wrap:wrap;
  padding:16px 32px;
  background:var(--bg);
  border-bottom:1px solid var(--line);
  position:sticky;top:81px;z-index:49;
}
.topic-btn{
  background:var(--card);border:1px solid var(--line);
  padding:10px 18px;border-radius:8px;
  font-family:inherit;font-size:14px;font-weight:500;
  color:var(--ink-soft);cursor:pointer;
  transition:all 0.2s;
}
.topic-btn:hover{border-color:var(--ink);color:var(--ink)}
.topic-btn.active{
  background:var(--ink);color:var(--bg);border-color:var(--ink);
  box-shadow:0 4px 12px rgba(26,31,46,0.15);
}

/* ============ TOPIC SECTIONS ============ */
main{max-width:920px;margin:0 auto;padding:40px 32px 80px}
.topic{animation:fadeUp 0.5s ease}
.topic.hidden{display:none}

@keyframes fadeUp{
  from{opacity:0;transform:translateY(20px)}
  to{opacity:1;transform:translateY(0)}
}

.topic-header{
  position:relative;margin-bottom:40px;
  padding-top:20px;
}
.topic-num{
  font-family:'Fraunces',serif;
  font-size:120px;font-weight:800;
  color:var(--accent-soft);
  position:absolute;top:-20px;right:0;
  line-height:1;letter-spacing:-0.04em;
  z-index:0;
  user-select:none;
}
.topic-header h2{
  font-family:'Fraunces',serif;
  font-size:42px;font-weight:800;
  letter-spacing:-0.03em;line-height:1.1;
  position:relative;z-index:1;
  margin-bottom:12px;
}
.topic-blurb{
  font-size:18px;color:var(--ink-soft);
  max-width:600px;position:relative;z-index:1;
}
.topic-blurb strong{color:var(--ink);font-weight:600}

/* ============ READING ============ */
.reading{
  background:var(--card);
  border:1px solid var(--line);
  border-radius:var(--radius);
  padding:32px 40px;
  box-shadow:var(--shadow);
  margin-bottom:32px;
}
.reading h3{
  font-family:'Fraunces',serif;
  font-size:24px;font-weight:600;
  margin-top:24px;margin-bottom:14px;
  letter-spacing:-0.02em;
  display:flex;align-items:center;gap:10px;
}
.reading h3:first-child{margin-top:0}
.reading h3::before{
  content:"";display:inline-block;
  width:4px;height:20px;background:var(--accent);border-radius:2px;
}
.reading p{margin-bottom:14px;font-size:16px}
.reading p strong{color:var(--ink);font-weight:600;background:var(--warn-soft);padding:1px 5px;border-radius:3px}
.reading p em{font-style:italic;color:var(--accent-deep)}
.rules{list-style:none;padding:0;margin:14px 0}
.rules li{
  padding:10px 14px 10px 38px;position:relative;
  background:var(--card-soft);border-radius:6px;margin-bottom:6px;
  font-size:15px;
}
.rules li::before{
  content:"→";position:absolute;left:14px;top:10px;
  color:var(--accent);font-weight:700;
}
.rules li code{
  font-family:'JetBrains Mono',monospace;
  background:var(--ink);color:var(--bg);
  padding:2px 8px;border-radius:4px;font-size:13px;
}
.rules li strong{color:var(--accent-deep);font-weight:700}
ol.rules{counter-reset:step}
ol.rules li::before{
  content:counter(step);counter-increment:step;
  background:var(--accent);color:var(--bg);
  width:20px;height:20px;border-radius:50%;
  display:flex;align-items:center;justify-content:center;
  font-size:11px;left:10px;top:12px;
}

/* ============ DIAGRAMS ============ */
.diagram{
  background:var(--card-soft);
  border:1px solid var(--line);
  border-radius:8px;
  padding:20px;margin:20px 0;
  overflow-x:auto;
}
.diagram svg{display:block;max-width:100%;height:auto}

/* ============ INTERACTIVE WIDGETS ============ */
.widget{
  background:linear-gradient(135deg,var(--ink) 0%,#2d3548 100%);
  color:var(--bg);
  border-radius:var(--radius);
  padding:32px 40px;
  margin-bottom:32px;
  box-shadow:var(--shadow);
}
.widget-header{margin-bottom:20px}
.widget-tag{
  display:inline-block;
  background:var(--accent);color:var(--bg);
  font-size:11px;font-weight:600;letter-spacing:0.12em;
  padding:4px 10px;border-radius:4px;margin-bottom:8px;
  text-transform:uppercase;
}
.widget h4{
  font-family:'Fraunces',serif;
  font-size:24px;font-weight:600;letter-spacing:-0.02em;
}
.widget-hint{
  margin-top:16px;
  font-size:14px;
  color:rgba(245,241,232,0.7);
  font-style:italic;
}

/* Binary converter */
.bits-row{display:flex;gap:8px;justify-content:center;flex-wrap:wrap}
.bit-cell{
  display:flex;flex-direction:column;align-items:center;gap:6px;
}
.bit-place{
  font-size:11px;color:rgba(245,241,232,0.5);
  font-family:'JetBrains Mono',monospace;
}
.bit-btn{
  width:56px;height:56px;
  background:rgba(245,241,232,0.05);
  border:2px solid rgba(245,241,232,0.2);
  border-radius:8px;
  font-family:'JetBrains Mono',monospace;
  font-size:28px;font-weight:600;
  color:var(--bg);cursor:pointer;
  transition:all 0.2s;
}
.bit-btn:hover{border-color:var(--accent);transform:translateY(-2px)}
.bit-btn.on{
  background:var(--accent);
  border-color:var(--accent);
  box-shadow:0 0 20px rgba(192,57,43,0.4);
}
.bin-result{
  display:flex;justify-content:space-around;
  margin-top:24px;padding-top:24px;
  border-top:1px solid rgba(245,241,232,0.1);
  text-align:center;
}
.bin-result .label{
  font-size:11px;color:rgba(245,241,232,0.5);
  text-transform:uppercase;letter-spacing:0.12em;
  font-weight:500;
}
.bin-out,.den-out{
  font-family:'JetBrains Mono',monospace;
  font-size:32px;font-weight:600;
  color:var(--bg);margin-top:6px;
}
.den-out{color:var(--accent);font-size:42px}

/* ============ QUESTIONS ============ */
.questions{display:flex;flex-direction:column;gap:20px;margin-top:24px}

.q-card{
  background:var(--card);
  border:1px solid var(--line);
  border-radius:var(--radius);
  padding:28px 32px;
  box-shadow:var(--shadow);
  position:relative;
  transition:border-color 0.3s;
}
.q-card.q-correct{border-color:var(--good);border-left-width:4px;border-left-style:solid}
.q-card.q-attempted{border-left:4px solid var(--warn)}

.q-num{
  display:inline-block;
  font-family:'JetBrains Mono',monospace;
  font-size:11px;font-weight:600;
  color:var(--accent);
  background:var(--accent-soft);
  padding:3px 10px;border-radius:4px;
  letter-spacing:0.08em;text-transform:uppercase;
  margin-bottom:10px;
}
.q-type-tag{
  display:inline-block;font-size:10px;
  background:var(--ink);color:var(--bg);
  padding:3px 8px;border-radius:3px;margin-left:6px;
  text-transform:uppercase;letter-spacing:0.1em;font-weight:600;
}

.q-text{
  font-size:18px;font-weight:500;
  margin-bottom:18px;line-height:1.5;
}
.q-text code{
  font-family:'JetBrains Mono',monospace;
  background:var(--card-soft);border:1px solid var(--line);
  padding:2px 8px;border-radius:4px;font-size:0.9em;
}

/* MCQ options */
.mcq-options{display:flex;flex-direction:column;gap:8px;margin-bottom:14px}
.mcq-option{
  display:flex;align-items:center;gap:12px;
  padding:12px 16px;
  background:var(--card-soft);border:1.5px solid var(--line);
  border-radius:8px;cursor:pointer;
  font-size:15px;
  transition:all 0.15s;
  text-align:left;font-family:inherit;
  color:var(--ink);
}
.mcq-option:hover{border-color:var(--ink-soft);background:var(--bg)}
.mcq-option.selected{border-color:var(--accent);background:var(--accent-soft)}
.mcq-option.correct{
  border-color:var(--good);background:var(--good-soft);color:var(--good);font-weight:600;
}
.mcq-option.wrong{
  border-color:var(--bad);background:var(--accent-soft);color:var(--accent-deep);
  text-decoration:line-through;
}
.mcq-option .letter{
  font-family:'JetBrains Mono',monospace;font-weight:700;
  background:var(--card);border:1px solid var(--line);
  width:26px;height:26px;border-radius:50%;
  display:flex;align-items:center;justify-content:center;
  font-size:12px;flex-shrink:0;
}

/* True/False */
.tf-buttons{display:flex;gap:12px;margin-bottom:14px}
.tf-buttons button{
  flex:1;padding:14px;
  background:var(--card-soft);border:1.5px solid var(--line);
  border-radius:8px;cursor:pointer;font-family:inherit;
  font-size:16px;font-weight:600;color:var(--ink);
  transition:all 0.2s;
}
.tf-buttons button:hover{border-color:var(--ink-soft)}
.tf-buttons button.selected{border-color:var(--accent);background:var(--accent-soft)}
.tf-buttons button.correct{border-color:var(--good);background:var(--good-soft);color:var(--good)}
.tf-buttons button.wrong{border-color:var(--bad);background:var(--accent-soft);color:var(--accent-deep)}

/* Fill-in / written */
.text-input{
  width:100%;padding:12px 16px;
  font-family:'JetBrains Mono',monospace;font-size:16px;
  background:var(--card-soft);
  border:1.5px solid var(--line);
  border-radius:8px;color:var(--ink);
  margin-bottom:12px;
  transition:border-color 0.2s;
}
.text-input:focus{outline:none;border-color:var(--accent);background:var(--card)}
textarea.text-input{
  font-family:inherit;min-height:90px;resize:vertical;
}

/* Match pairs */
.match-wrap{
  display:grid;grid-template-columns:1fr 1fr;gap:14px;margin-bottom:14px;
}
.match-col h5{
  font-size:11px;text-transform:uppercase;letter-spacing:0.1em;
  color:var(--ink-soft);margin-bottom:8px;font-weight:600;
}
.match-item{
  padding:10px 14px;background:var(--card-soft);
  border:1.5px solid var(--line);border-radius:6px;
  margin-bottom:6px;cursor:pointer;font-size:14px;
  transition:all 0.15s;user-select:none;
}
.match-item:hover{border-color:var(--ink-soft)}
.match-item.selected{border-color:var(--accent);background:var(--accent-soft)}
.match-item.matched{
  border-color:var(--good);background:var(--good-soft);
  cursor:default;color:var(--good);font-weight:600;
}
.match-item.matched .pair-num{
  display:inline-flex;align-items:center;justify-content:center;
  background:var(--good);color:var(--bg);
  border-radius:50%;width:18px;height:18px;
  font-family:'JetBrains Mono',monospace;font-size:10px;
  margin-right:8px;
}

/* Submit */
.q-actions{display:flex;align-items:center;gap:12px;margin-top:8px;flex-wrap:wrap}
.submit-btn{
  background:var(--ink);color:var(--bg);
  border:none;padding:10px 22px;border-radius:6px;
  font-family:inherit;font-size:14px;font-weight:600;
  cursor:pointer;transition:all 0.2s;
}
.submit-btn:hover{background:var(--accent);transform:translateY(-1px)}
.submit-btn:disabled{
  background:var(--ink-faint);cursor:not-allowed;transform:none;
}
.attempts{
  font-size:12px;color:var(--ink-soft);
  font-family:'JetBrains Mono',monospace;
}

/* Feedback */
.feedback{
  margin-top:14px;padding:14px 16px;border-radius:8px;
  font-size:14px;line-height:1.5;
  display:none;
  animation:slideIn 0.3s ease;
}
@keyframes slideIn{from{opacity:0;transform:translateY(-6px)}to{opacity:1;transform:translateY(0)}}
.feedback.show{display:block}
.feedback.fb-correct{
  background:var(--good-soft);color:var(--good);
  border-left:3px solid var(--good);
}
.feedback.fb-wrong{
  background:var(--warn-soft);color:var(--warn);
  border-left:3px solid var(--warn);
}
.feedback.fb-explain{
  background:var(--card-soft);color:var(--ink);
  border-left:3px solid var(--accent);
  margin-top:8px;
}
.feedback strong{font-weight:700}
.feedback .fb-title{
  display:block;font-size:11px;text-transform:uppercase;
  letter-spacing:0.1em;font-weight:700;margin-bottom:4px;
}

/* Loading spinner */
.spinner{
  display:inline-block;width:14px;height:14px;
  border:2px solid var(--ink-faint);border-top-color:var(--accent);
  border-radius:50%;animation:spin 0.8s linear infinite;
  margin-right:8px;vertical-align:middle;
}
@keyframes spin{to{transform:rotate(360deg)}}

/* ============ TOAST ============ */
.toast{
  position:fixed;bottom:24px;left:50%;
  transform:translateX(-50%) translateY(120%);
  background:var(--ink);color:var(--bg);
  padding:12px 24px;border-radius:24px;
  font-size:14px;font-weight:500;
  box-shadow:0 8px 24px rgba(0,0,0,0.2);
  transition:transform 0.3s ease;z-index:100;
}
.toast.show{transform:translateX(-50%) translateY(0)}

/* ============ FOOTER ============ */
footer{
  text-align:center;padding:24px;
  color:var(--ink-faint);font-size:12px;
}

/* ============ MOBILE ============ */
@media (max-width:680px){
  .topbar{padding:14px 16px;flex-direction:column;align-items:flex-start}
  .progress-wrap{width:100%;justify-content:space-between}
  .progress-bar{flex:1;width:auto;margin:0 12px}
  .topic-nav{padding:12px 16px;top:130px;overflow-x:auto;flex-wrap:nowrap;-webkit-overflow-scrolling:touch}
  .topic-btn{flex-shrink:0;font-size:13px;padding:8px 14px}
  main{padding:24px 16px 60px}
  .topic-num{font-size:80px;top:-10px}
  .topic-header h2{font-size:30px}
  .topic-blurb{font-size:16px}
  .reading,.widget{padding:24px 20px}
  .q-card{padding:22px 20px}
  .q-text{font-size:16px}
  .match-wrap{grid-template-columns:1fr}
  .bit-btn{width:42px;height:42px;font-size:22px}
  .bit-place{font-size:9px}
  .den-out{font-size:32px}
}