:root {
  --bg:#09090f;--surface:#0e0e1a;--card:#13131f;--border:#1e1e30;--border2:#252538;
  --text:#e8e8f0;--muted:#7070a0;--dim:#3a3a5c;
  --amber:#f5a623;--amber-dim:rgba(245,166,35,0.12);--amber-border:rgba(245,166,35,0.25);
  --teal:#2dd4bf;--teal-dim:rgba(45,212,191,0.1);--teal-border:rgba(45,212,191,0.2);
  --red:#f87171;--red-dim:rgba(248,113,113,0.1);
  --blue:#60a5fa;--blue-dim:rgba(96,165,250,0.1);
  --purple:#a78bfa;--purple-dim:rgba(167,139,250,0.1);
  --green:#4ade80;--green-dim:rgba(74,222,128,0.08);
}
*,*::before,*::after{box-sizing:border-box;margin:0;padding:0}
html{scroll-behavior:smooth}
body{font-family:'Syne',sans-serif;background:var(--bg);color:var(--text);line-height:1.65;overflow-x:hidden}
header{border-bottom:1px solid var(--border);padding:0 48px;height:58px;display:flex;align-items:center;justify-content:space-between;position:sticky;top:0;z-index:200;background:rgba(9,9,15,0.92);backdrop-filter:blur(12px)}
.logo{display:flex;align-items:center;gap:10px;font-size:13px;font-weight:700;letter-spacing:.05em;color:var(--text)}
.logo-mark{width:28px;height:28px;background:linear-gradient(135deg,var(--amber),#ff6b35);border-radius:6px;display:flex;align-items:center;justify-content:center;font-size:14px;font-weight:800;color:#000}
.header-right{display:flex;align-items:center;gap:24px}
.progress-pill{display:flex;align-items:center;gap:10px;font-size:12px;color:var(--muted);font-weight:600}
.progress-track{width:120px;height:4px;background:var(--border2);border-radius:2px;overflow:hidden}
.progress-fill{height:100%;background:linear-gradient(90deg,var(--amber),var(--teal));border-radius:2px;transition:width .5s ease;width:0%}
.badge-level{font-size:11px;font-weight:700;letter-spacing:.08em;padding:3px 10px;border-radius:4px;background:var(--amber-dim);color:var(--amber);border:1px solid var(--amber-border);text-transform:uppercase}
.shell{display:flex;min-height:calc(100vh - 58px)}
.sidebar{width:260px;flex-shrink:0;border-right:1px solid var(--border);padding:28px 0;position:sticky;top:58px;height:calc(100vh - 58px);overflow-y:auto}
.sidebar-section-label{font-size:10px;font-weight:700;letter-spacing:.14em;text-transform:uppercase;color:var(--dim);padding:0 20px;margin-bottom:8px;margin-top:20px}
.sidebar-section-label:first-child{margin-top:0}
.nav-item{display:flex;align-items:center;gap:10px;padding:9px 20px;cursor:pointer;font-size:13px;font-weight:600;color:var(--muted);transition:all .15s;border:none;background:none;width:100%;text-align:left;position:relative}
.nav-item:hover{color:var(--text);background:rgba(255,255,255,.03)}
.nav-item.active{color:var(--amber);background:var(--amber-dim);border-right:2px solid var(--amber)}
.nav-item.done{color:var(--teal)}
.nav-item.done::after{content:'✓';font-size:11px;margin-left:auto;color:var(--teal)}
.nav-num{width:20px;height:20px;border-radius:4px;background:var(--border2);font-size:10px;font-weight:700;display:flex;align-items:center;justify-content:center;color:var(--dim);flex-shrink:0}
.nav-item.active .nav-num{background:var(--amber);color:#000}
.nav-item.done .nav-num{background:var(--teal-dim);color:var(--teal);border:1px solid var(--teal-border)}
.nav-tag{margin-left:auto;font-size:10px;font-weight:700;padding:2px 6px;border-radius:3px;text-transform:uppercase;letter-spacing:.06em}
.nav-tag.adv{background:rgba(248,113,113,0.12);color:var(--red)}
.main{flex:1;min-width:0;padding:48px 60px 80px}
.lesson{display:none}
.lesson.active{display:block;animation:slideIn .3s ease}
@keyframes slideIn{from{opacity:0;transform:translateY(8px)}to{opacity:1;transform:translateY(0)}}
.lesson-eyebrow{display:flex;align-items:center;gap:12px;margin-bottom:16px}
.eyebrow-tag{font-size:11px;font-weight:700;letter-spacing:.1em;text-transform:uppercase;color:var(--amber)}
.eyebrow-sep{color:var(--dim);font-size:12px}
.eyebrow-topic{font-size:11px;color:var(--muted);letter-spacing:.05em}
.lesson h2{font-family:'Instrument Serif',serif;font-size:clamp(2rem,3.5vw,3rem);font-weight:400;line-height:1.15;margin-bottom:16px;letter-spacing:-.01em}
.lesson-lead{font-size:1rem;color:var(--muted);max-width:640px;margin-bottom:40px;line-height:1.75;border-left:2px solid var(--border2);padding-left:16px}
.prose{max-width:780px}
.prose p{font-size:.95rem;color:#c0c0d8;line-height:1.8;margin-bottom:18px}
.prose h3{font-family:'Instrument Serif',serif;font-size:1.35rem;font-weight:400;margin:36px 0 14px;color:var(--text)}
.prose ul,.prose ol{padding-left:22px;margin-bottom:18px}
.prose li{font-size:.93rem;color:#b0b0cc;margin-bottom:8px;line-height:1.7}
.prose strong{color:var(--text);font-weight:700}
.prose code{font-family:'DM Mono',monospace;font-size:.83em;background:var(--border);border:1px solid var(--border2);color:var(--amber);padding:1px 6px;border-radius:4px}
.code-wrap{margin:24px 0}
.code-header{display:flex;align-items:center;justify-content:space-between;background:#0d0d18;border:1px solid var(--border);border-bottom:none;padding:10px 18px;border-radius:8px 8px 0 0}
.code-filename{font-family:'DM Mono',monospace;font-size:12px;color:var(--muted);display:flex;align-items:center;gap:8px}
.code-filename::before{content:'';width:10px;height:10px;border-radius:50%;background:var(--amber);flex-shrink:0}
.code-meta{font-size:11px;color:var(--dim);letter-spacing:.06em;text-transform:uppercase}
pre{background:#080812;border:1px solid var(--border);border-radius:0 0 8px 8px;padding:22px 24px;overflow-x:auto;font-family:'DM Mono',monospace;font-size:.84rem;line-height:1.9}
.kw{color:#c084fc}.cl{color:#fbbf24}.fn{color:#34d399}.str{color:#fb923c}.cm{color:#4b5380;font-style:italic}.num{color:#f472b6}.ann{color:#60a5fa}.op{color:#94a3b8}
.callout{display:flex;gap:14px;padding:18px 20px;border-radius:8px;margin:24px 0;font-size:.92rem;line-height:1.75;max-width:780px}
.callout-icon{font-size:18px;flex-shrink:0;margin-top:1px}
.callout-body{flex:1}
.callout-body strong{display:block;font-size:.93rem;margin-bottom:5px}
.callout.warn{background:rgba(245,166,35,.07);border:1px solid var(--amber-border)}
.callout.warn strong{color:var(--amber)}
.callout.tip{background:var(--teal-dim);border:1px solid var(--teal-border)}
.callout.tip strong{color:var(--teal)}
.callout.danger{background:var(--red-dim);border:1px solid rgba(248,113,113,.2)}
.callout.danger strong{color:var(--red)}
.callout.info{background:var(--blue-dim);border:1px solid rgba(96,165,250,.2)}
.callout.info strong{color:var(--blue)}
.callout.pattern{background:var(--purple-dim);border:1px solid rgba(167,139,250,.2)}
.callout.pattern strong{color:var(--purple)}
.callout p{color:#a0a0c0;margin:0}
.callout p+p{margin-top:8px}
.concept-grid{display:grid;grid-template-columns:repeat(auto-fit,minmax(200px,1fr));gap:14px;margin:24px 0}
.concept-card{background:var(--card);border:1px solid var(--border);border-radius:8px;padding:18px;transition:border-color .2s}
.concept-card:hover{border-color:var(--border2)}
.concept-card-label{font-size:10px;font-weight:700;letter-spacing:.1em;text-transform:uppercase;margin-bottom:8px}
.concept-card h4{font-size:.95rem;font-weight:700;margin-bottom:6px}
.concept-card p{font-size:.82rem;color:var(--muted);line-height:1.6}
.table-wrap{overflow-x:auto;margin:20px 0;max-width:780px}
table{width:100%;border-collapse:collapse;font-size:.88rem}
th{text-align:left;padding:10px 16px;font-size:11px;font-weight:700;letter-spacing:.08em;text-transform:uppercase;color:var(--muted);border-bottom:1px solid var(--border2);background:var(--surface)}
td{padding:11px 16px;border-bottom:1px solid var(--border);color:#b0b0cc;vertical-align:top}
td:first-child{color:var(--text);font-weight:600;font-family:'DM Mono',monospace;font-size:.83rem}
tr:last-child td{border-bottom:none}
.quiz-block{background:var(--card);border:1px solid var(--border);border-radius:10px;padding:28px;margin:36px 0;max-width:780px}
.quiz-label{font-size:10px;font-weight:700;letter-spacing:.12em;text-transform:uppercase;color:var(--amber);margin-bottom:14px}
.quiz-q{font-size:.97rem;font-weight:600;margin-bottom:20px;line-height:1.6}
.quiz-options{display:flex;flex-direction:column;gap:10px}
.quiz-opt{background:var(--surface);border:1px solid var(--border2);border-radius:6px;padding:12px 16px;cursor:pointer;font-family:'Syne',sans-serif;font-size:.9rem;font-weight:500;color:var(--muted);text-align:left;transition:all .15s}
.quiz-opt:hover:not(:disabled){border-color:var(--amber);color:var(--text)}
.quiz-opt.correct{border-color:var(--teal);color:var(--teal);background:var(--teal-dim)}
.quiz-opt.wrong{border-color:var(--red);color:var(--red);background:var(--red-dim)}
.quiz-opt:disabled{cursor:default}
.quiz-feedback{margin-top:16px;padding:12px 16px;border-radius:6px;font-size:.88rem;font-weight:600;display:none}
.quiz-feedback.show{display:block}
.quiz-feedback.ok{background:var(--teal-dim);color:var(--teal);border:1px solid var(--teal-border)}
.quiz-feedback.bad{background:var(--red-dim);color:var(--red);border:1px solid rgba(248,113,113,.2)}
.challenge{background:linear-gradient(135deg,rgba(15,15,28,1),rgba(12,18,28,1));border:1px solid var(--border2);border-radius:10px;padding:28px;margin:32px 0;max-width:780px;position:relative;overflow:hidden}
.challenge::before{content:'';position:absolute;top:0;left:0;right:0;height:2px;background:linear-gradient(90deg,var(--amber),var(--teal))}
.challenge-label{font-size:10px;font-weight:700;letter-spacing:.12em;text-transform:uppercase;color:var(--amber);margin-bottom:12px}
.challenge h4{font-size:1rem;font-weight:700;margin-bottom:10px}
.challenge p{font-size:.9rem;color:#9090b8;line-height:1.75;margin-bottom:10px}
.challenge ul{padding-left:18px}
.challenge li{font-size:.88rem;color:#8888b0;margin-bottom:6px;line-height:1.65}
.challenge code{font-family:'DM Mono',monospace;font-size:.82em;color:var(--teal);background:var(--teal-dim);padding:1px 6px;border-radius:3px}
.solid-grid{display:flex;flex-direction:column;gap:2px;margin:24px 0;max-width:780px}
.solid-row{display:flex;gap:0;border:1px solid var(--border);overflow:hidden}
.solid-row:first-child{border-radius:8px 8px 0 0}
.solid-row:last-child{border-radius:0 0 8px 8px}
.solid-letter{width:48px;flex-shrink:0;background:var(--amber-dim);color:var(--amber);font-size:1.5rem;font-weight:800;display:flex;align-items:center;justify-content:center;border-right:1px solid var(--amber-border);font-family:'Instrument Serif',serif}
.solid-body{padding:14px 18px;flex:1}
.solid-body h4{font-size:.93rem;font-weight:700;margin-bottom:4px}
.solid-body p{font-size:.86rem;color:var(--muted);margin:0;line-height:1.6}
.pattern-grid{display:grid;grid-template-columns:repeat(auto-fit,minmax(220px,1fr));gap:14px;margin:24px 0}
.pattern-card{background:var(--card);border:1px solid var(--border);border-radius:8px;padding:20px;transition:border-color .2s}
.pattern-card:hover{border-color:var(--purple)}
.pattern-type{font-size:10px;font-weight:700;letter-spacing:.1em;text-transform:uppercase;color:var(--purple);margin-bottom:8px}
.pattern-card h4{font-size:.95rem;font-weight:700;margin-bottom:6px}
.pattern-card p{font-size:.83rem;color:var(--muted);line-height:1.6}
.lesson-nav{display:flex;justify-content:space-between;align-items:center;margin-top:64px;padding-top:28px;border-top:1px solid var(--border);max-width:780px}
.btn{font-family:'Syne',sans-serif;font-size:13px;font-weight:700;padding:11px 22px;border-radius:6px;cursor:pointer;border:none;transition:all .15s;letter-spacing:.03em}
.btn-next{background:var(--amber);color:#000}
.btn-next:hover:not(:disabled){background:#f7b93e;transform:translateY(-1px)}
.btn-prev{background:var(--card);color:var(--muted);border:1px solid var(--border2)}
.btn-prev:hover{color:var(--text);border-color:var(--amber)}
.btn:disabled{opacity:.3;cursor:not-allowed;transform:none!important}
::-webkit-scrollbar{width:5px;height:5px}
::-webkit-scrollbar-track{background:transparent}
::-webkit-scrollbar-thumb{background:var(--border2);border-radius:3px}
@media(max-width:900px){.sidebar{display:none}.main{padding:32px 24px 60px}header{padding:0 20px}}
/* Mobile Responsive Overrides */
@media (max-width: 768px) {
    .shell, .layout { 
        flex-direction: column !important; 
    }
    .sidebar { 
        width: 100% !important; 
        position: static !important;
        margin-bottom: 20px;
    }
    .main { 
        width: 100% !important; 
        padding: 15px !important;
    }
    .lesson-nav { 
        flex-direction: column; 
        gap: 10px; 
    }
    button, .nav-btn, .btn { 
        min-height: 44px !important; 
        padding: 12px !important;
    }
}