:root{
  --bg:#0f1226; --bg2:#171a35; --card:#1e2247; --card2:#262b57;
  --ink:#eef1ff; --muted:#a8b0d8; --line:#33396f;
  --brand:#6c8cff; --brand2:#9b6cff; --good:#36d399; --bad:#ff6b81; --warn:#ffd166;
  --code-bg:#0b0e22;
  --r:16px; --shadow:0 10px 30px rgba(0,0,0,.35);
}
*{box-sizing:border-box}
html,body{margin:0;padding:0}
body{
  font-family:'Heebo',system-ui,Arial,sans-serif;
  background:radial-gradient(1200px 600px at 80% -10%, #23285a 0%, var(--bg) 55%);
  color:var(--ink); min-height:100vh; line-height:1.7;
}
h1,h2,h3,h4{line-height:1.3;margin:.2em 0 .4em}
code,kbd,.mono{font-family:'Fira Code',monospace}
a{color:var(--brand)}

/* ===== Topbar ===== */
.topbar{
  position:sticky;top:0;z-index:40;display:flex;align-items:center;gap:14px;
  padding:12px 18px;background:rgba(15,18,38,.85);backdrop-filter:blur(10px);
  border-bottom:1px solid var(--line);
}
.brand{display:flex;align-items:center;gap:12px}
.brand h1{font-size:1.15rem;margin:0}
.brand p{margin:0;font-size:.78rem;color:var(--muted)}
.logo{font-size:1.8rem}
.menu-toggle{display:none;background:var(--card);border:1px solid var(--line);color:var(--ink);
  font-size:1.2rem;border-radius:10px;width:42px;height:42px;cursor:pointer}
.progress-pill{margin-inline-start:auto;background:linear-gradient(90deg,var(--brand),var(--brand2));
  color:#fff;font-weight:700;padding:8px 16px;border-radius:999px;font-size:.9rem;box-shadow:var(--shadow)}

/* ===== Layout ===== */
.layout{display:grid;grid-template-columns:300px 1fr;gap:0;align-items:start}
.sidebar{
  position:sticky;top:67px;height:calc(100vh - 67px);overflow-y:auto;
  padding:16px;border-inline-end:1px solid var(--line);background:rgba(23,26,53,.5)
}
.content{padding:28px clamp(16px,4vw,56px);max-width:1100px;margin:0 auto;width:100%}

/* ===== Sidebar nav ===== */
.mod{margin-bottom:14px}
.mod-title{display:flex;align-items:center;gap:10px;font-weight:800;font-size:.98rem;
  padding:10px 12px;border-radius:12px;background:var(--card);border:1px solid var(--line)}
.mod-title .ico{font-size:1.2rem}
.mod-title .mbar{margin-inline-start:auto;font-size:.72rem;color:var(--muted)}
.lessons{list-style:none;margin:6px 0 0;padding:0}
.lessons li{margin:3px 0}
.lessons button{
  width:100%;text-align:start;background:transparent;border:none;color:var(--muted);
  padding:8px 12px 8px 34px;border-radius:10px;cursor:pointer;font-size:.9rem;position:relative;
  display:flex;align-items:center;gap:8px
}
.lessons button:hover{background:var(--card2);color:var(--ink)}
.lessons button.active{background:linear-gradient(90deg,rgba(108,140,255,.25),transparent);
  color:var(--ink);font-weight:600;box-shadow:inset 3px 0 0 var(--brand)}
.lessons button .chk{position:absolute;inset-inline-start:10px;font-size:.85rem}
.done .chk{color:var(--good)}

/* ===== Content blocks ===== */
.lesson-head{margin-bottom:10px}
.lesson-head .crumb{color:var(--muted);font-size:.82rem;letter-spacing:.04em}
.lesson-head h2{font-size:1.7rem;background:linear-gradient(90deg,var(--ink),#c9d2ff);
  -webkit-background-clip:text;background-clip:text}
.card{background:var(--card);border:1px solid var(--line);border-radius:var(--r);
  padding:20px 22px;margin:18px 0;box-shadow:var(--shadow)}
.card h3{font-size:1.2rem;color:#cdd6ff}
.tag{display:inline-block;font-size:.72rem;padding:3px 10px;border-radius:999px;
  background:var(--card2);color:var(--muted);border:1px solid var(--line);margin-inline-end:6px}
.callout{border-inline-start:4px solid var(--brand);background:rgba(108,140,255,.08);
  padding:12px 16px;border-radius:10px;margin:14px 0}
.callout.tip{border-color:var(--good);background:rgba(54,211,153,.08)}
.callout.warn{border-color:var(--warn);background:rgba(255,209,102,.08)}
.callout .ttl{font-weight:700;margin-bottom:4px;display:block}
.simple{font-size:1.05rem}
.simple b{color:#fff}
ul.clean{padding-inline-start:22px}
ul.clean li{margin:6px 0}

/* analogy box */
.analogy{display:flex;gap:14px;align-items:flex-start;background:linear-gradient(135deg,rgba(155,108,255,.12),rgba(108,140,255,.06));
  border:1px solid var(--line);border-radius:14px;padding:14px 16px;margin:14px 0}
.analogy .emoji{font-size:2rem;line-height:1}

/* code */
pre{background:var(--code-bg);border:1px solid var(--line);border-radius:12px;
  padding:16px;overflow:auto;direction:ltr;text-align:left;font-size:.9rem}
pre code{color:#e6ebff}
.tok-kw{color:#ff9ecb}.tok-type{color:#7ee0ff}.tok-str{color:#b9f18d}
.tok-num{color:#ffd28a}.tok-com{color:#7480b0;font-style:italic}.tok-fn{color:#ffd166}

/* trace table */
.trace{overflow:auto;margin:14px 0}
table.trace-tbl{border-collapse:collapse;width:100%;font-size:.88rem;direction:ltr}
table.trace-tbl th,table.trace-tbl td{border:1px solid var(--line);padding:8px 10px;text-align:center}
table.trace-tbl th{background:var(--card2);color:#cdd6ff}
table.trace-tbl tr:nth-child(even) td{background:rgba(255,255,255,.02)}
.hl{background:rgba(255,209,102,.25)!important;font-weight:700}

/* demo container */
.demo{background:linear-gradient(160deg,#13173a,#0e1130);border:1px solid var(--line);
  border-radius:14px;padding:18px;margin:18px 0}
.demo h4{margin-top:0;color:#cdd6ff;display:flex;align-items:center;gap:8px}
.demo-canvas{width:100%;background:var(--code-bg);border:1px solid var(--line);border-radius:10px}
.controls{display:flex;flex-wrap:wrap;gap:8px;margin:12px 0;align-items:center}
.btn{background:linear-gradient(90deg,var(--brand),var(--brand2));color:#fff;border:none;
  padding:9px 16px;border-radius:10px;cursor:pointer;font-weight:600;font-size:.9rem;font-family:inherit}
.btn:hover{filter:brightness(1.1)}
.btn.ghost{background:var(--card);border:1px solid var(--line);color:var(--ink)}
.btn.sm{padding:6px 12px;font-size:.82rem}
.btn:disabled{opacity:.45;cursor:not-allowed}
input[type=text],input[type=number],select,textarea{
  background:var(--code-bg);border:1px solid var(--line);color:var(--ink);border-radius:9px;
  padding:8px 12px;font-family:inherit;font-size:.9rem}
input.mono{font-family:'Fira Code',monospace}
input[type=range]{accent-color:var(--brand)}
.statline{font-size:.85rem;color:var(--muted);margin-top:8px}
.statline b{color:var(--ink)}
.badge{display:inline-block;padding:2px 9px;border-radius:8px;font-size:.78rem;font-weight:700}
.badge.o1{background:rgba(54,211,153,.2);color:var(--good)}
.badge.on{background:rgba(255,209,102,.2);color:var(--warn)}
.badge.on2{background:rgba(255,107,129,.2);color:var(--bad)}

/* quiz */
.quiz .q{font-weight:600;margin-bottom:10px}
.quiz .opts{display:flex;flex-direction:column;gap:8px;margin:10px 0}
.opt{display:flex;gap:10px;align-items:flex-start;background:var(--card2);border:1px solid var(--line);
  border-radius:10px;padding:10px 14px;cursor:pointer;transition:.15s}
.opt:hover{border-color:var(--brand)}
.opt.correct{border-color:var(--good);background:rgba(54,211,153,.14)}
.opt.wrong{border-color:var(--bad);background:rgba(255,107,129,.14)}
.opt .mk{font-weight:800}
.solution{margin-top:12px;border-top:1px dashed var(--line);padding-top:12px;display:none}
.solution.show{display:block}
.quiz-nav{display:flex;justify-content:space-between;align-items:center;margin-top:14px}
.qcount{color:var(--muted);font-size:.85rem}

.lesson-foot{display:flex;justify-content:space-between;margin:30px 0 60px;gap:12px}
.lesson-foot .btn{min-width:150px;text-align:center}

/* ===== Tutor ===== */
.tutor-fab{position:fixed;inset-block-end:22px;inset-inline-start:22px;z-index:50;
  background:linear-gradient(90deg,var(--brand),var(--brand2));color:#fff;border:none;
  border-radius:999px;padding:12px 18px;font-size:1.1rem;cursor:pointer;box-shadow:var(--shadow);
  display:flex;align-items:center;gap:8px;font-family:inherit}
.tutor-fab span{font-size:.9rem;font-weight:700}
.tutor-panel{position:fixed;inset-block-end:80px;inset-inline-start:22px;z-index:50;width:min(380px,92vw);
  height:min(540px,75vh);background:var(--bg2);border:1px solid var(--line);border-radius:18px;
  box-shadow:var(--shadow);display:flex;flex-direction:column;overflow:hidden}
.tutor-head{display:flex;justify-content:space-between;align-items:center;padding:12px 16px;
  background:linear-gradient(90deg,var(--brand),var(--brand2));font-weight:700}
.tutor-head button{background:transparent;border:none;color:#fff;font-size:1.1rem;cursor:pointer}
.tutor-msgs{flex:1;overflow-y:auto;padding:14px;display:flex;flex-direction:column;gap:10px}
.msg{max-width:85%;padding:10px 14px;border-radius:14px;font-size:.92rem;white-space:pre-wrap}
.msg.bot{background:var(--card2);border:1px solid var(--line);align-self:flex-start;border-bottom-inline-start-radius:4px}
.msg.user{background:linear-gradient(90deg,var(--brand),var(--brand2));align-self:flex-end;border-bottom-inline-end-radius:4px}
.msg.sys{background:rgba(255,209,102,.1);border:1px solid var(--warn);align-self:center;font-size:.84rem;color:var(--warn)}
.tutor-input{display:flex;gap:8px;padding:10px;border-top:1px solid var(--line)}
.tutor-input textarea{flex:1;resize:none}
.tutor-input button{background:linear-gradient(90deg,var(--brand),var(--brand2));color:#fff;border:none;
  border-radius:10px;padding:0 16px;cursor:pointer;font-weight:700}
.tutor-foot{padding:6px 12px;border-top:1px solid var(--line);text-align:center}
.link-btn{background:none;border:none;color:var(--muted);cursor:pointer;font-size:.8rem;text-decoration:underline}
.typing{display:inline-flex;gap:3px}.typing i{width:6px;height:6px;border-radius:50%;background:var(--muted);animation:bl 1s infinite}
.typing i:nth-child(2){animation-delay:.2s}.typing i:nth-child(3){animation-delay:.4s}
@keyframes bl{0%,80%,100%{opacity:.2}40%{opacity:1}}

.hidden{display:none!important}

/* welcome */
.welcome{text-align:center;padding:40px 20px}
.welcome .big{font-size:3rem}
.modgrid{display:grid;grid-template-columns:repeat(auto-fit,minmax(220px,1fr));gap:14px;margin-top:24px;text-align:start}
.modcard{background:var(--card);border:1px solid var(--line);border-radius:14px;padding:18px;cursor:pointer;transition:.15s}
.modcard:hover{transform:translateY(-3px);border-color:var(--brand)}
.modcard .ico{font-size:2rem}
.modcard h4{margin:8px 0 4px}
.modcard p{color:var(--muted);font-size:.86rem;margin:0}

/* ===== Mobile ===== */
@media(max-width:880px){
  .layout{grid-template-columns:1fr}
  .menu-toggle{display:block}
  .sidebar{position:fixed;inset-block-start:67px;inset-inline-start:0;width:280px;z-index:30;
    transform:translateX(105%);transition:.25s;height:calc(100vh - 67px)}
  html[dir=rtl] .sidebar{transform:translateX(105%)}
  .sidebar.open{transform:translateX(0)}
  .brand h1{font-size:1rem}
}