:root {
  --bg:#1e1f22;--surface:#2b2d30;--panel:#1e1f22;--card:#2b2d30;
  --border:#3c3f41;--border2:#4e5157;
  --text:#dfe1e5;--body:#abb2bf;--muted:#6e7480;--dim:#3c3f41;
  --ij:#4d8ccd;--ij-dim:rgba(77,140,205,0.12);--ij-border:rgba(77,140,205,0.28);
  --ij-light:rgba(77,140,205,0.06);
  --green:#5fad6e;--green-dim:rgba(95,173,110,0.1);--green-border:rgba(95,173,110,0.25);
  --yellow:#e0ac47;--yellow-dim:rgba(224,172,71,0.1);--yellow-border:rgba(224,172,71,0.25);
  --red:#e06c75;--red-dim:rgba(224,108,117,0.1);--red-border:rgba(224,108,117,0.25);
  --purple:#c678dd;--orange:#d19a66;
  --kbd-bg:#3c3f41;--kbd-border:#555;
}
*,*::before,*::after{box-sizing:border-box;margin:0;padding:0}
html{scroll-behavior:smooth}
body{font-family:'Inter',sans-serif;background:var(--bg);color:var(--text);line-height:1.6;overflow-x:hidden}

/* HEADER — mimics IntelliJ toolbar */
header{background:#3c3f41;border-bottom:1px solid #2b2d30;padding:0 0 0 0;height:56px;display:flex;align-items:stretch;position:sticky;top:0;z-index:100}
.hdr-logo{display:flex;align-items:center;gap:10px;padding:0 20px;border-right:1px solid var(--border)}
.logo-mark{width:28px;height:28px;background:linear-gradient(135deg,#FF318C,#FF7B00,#FFD200,#00B2FF);border-radius:5px;flex-shrink:0}
.logo-text{font-family:'JetBrains Mono',monospace;font-size:13px;font-weight:700;color:var(--text)}
.hdr-tabs{display:flex;align-items:stretch;flex:1;overflow:hidden}
.hdr-tab{display:flex;align-items:center;padding:0 18px;font-size:12px;color:var(--muted);border-right:1px solid var(--border);cursor:default;white-space:nowrap}
.hdr-tab.active-tab{color:var(--text);background:var(--bg)}
.hdr-right{display:flex;align-items:center;gap:16px;padding:0 20px;margin-left:auto;border-left:1px solid var(--border)}
.prog-track{width:110px;height:4px;background:var(--border2);border-radius:2px;overflow:hidden}
.prog-fill{height:100%;background:linear-gradient(90deg,var(--ij),#6ab0f5);border-radius:2px;transition:width .5s ease;width:0%}
.prog-pct{font-family:'JetBrains Mono',monospace;font-size:11px;color:var(--ij);font-weight:700;min-width:30px}

/* LAYOUT */
.shell{display:flex;min-height:calc(100vh - 56px)}

/* SIDEBAR — mimics IntelliJ project panel */
.sidebar{width:252px;flex-shrink:0;border-right:1px solid var(--border);background:var(--surface);padding:0;position:sticky;top:56px;height:calc(100vh - 56px);overflow-y:auto}
.sb-panel-header{background:#3c3f41;border-bottom:1px solid var(--border);padding:8px 12px;font-size:11px;font-weight:700;color:var(--muted);letter-spacing:.06em;text-transform:uppercase;display:flex;align-items:center;gap:6px}
.sb-panel-header::before{content:'';width:3px;height:12px;background:var(--ij);border-radius:2px}
.sb-section{font-size:10px;font-weight:700;letter-spacing:.1em;text-transform:uppercase;color:var(--muted);padding:14px 14px 5px;display:flex;align-items:center;gap:6px}
.sb-section::before{content:'▾';font-size:9px;color:var(--muted)}
.nav-btn{display:flex;align-items:center;gap:8px;padding:6px 14px 6px 24px;width:100%;border:none;background:none;cursor:pointer;font-family:'Inter',sans-serif;font-size:12px;font-weight:500;color:var(--muted);text-align:left;transition:all .1s;line-height:1.4}
.nav-btn:hover{color:var(--text);background:rgba(77,140,205,0.08)}
.nav-btn.active{color:#fff;background:var(--ij);font-weight:600}
.nav-btn.done{color:var(--green)}
.nav-btn.done::after{content:'✓';margin-left:auto;font-size:10px;color:var(--green)}
.nav-ico{font-size:13px;flex-shrink:0}

/* MAIN */
.main{flex:1;min-width:0;padding:44px 56px 80px}

/* LESSON */
.lesson{display:none}
.lesson.active{display:block;animation:fadeUp .25s ease}
@keyframes fadeUp{from{opacity:0;transform:translateY(6px)}to{opacity:1;transform:translateY(0)}}
.lesson-eyebrow{display:flex;align-items:center;gap:10px;margin-bottom:12px}
.ey-num{font-family:'JetBrains Mono',monospace;font-size:11px;font-weight:700;color:var(--ij);letter-spacing:.06em}
.ey-dot{width:3px;height:3px;background:var(--muted);border-radius:50%}
.ey-cat{font-family:'JetBrains Mono',monospace;font-size:11px;color:var(--muted)}
.lesson h2{font-family:'Inter',sans-serif;font-size:clamp(1.55rem,2.5vw,2rem);font-weight:700;color:var(--text);line-height:1.2;margin-bottom:14px;letter-spacing:-.02em}
.lesson h2 em{color:var(--ij);font-style:normal}
.lesson-intro{font-size:.93rem;color:var(--muted);max-width:640px;line-height:1.8;margin-bottom:36px;padding-left:14px;border-left:2px solid var(--ij)}

/* PROSE */
.prose{max-width:740px}
.prose p{font-size:.92rem;color:var(--body);line-height:1.85;margin-bottom:16px}
.prose h3{font-family:'Inter',sans-serif;font-size:.97rem;font-weight:700;color:var(--text);margin:28px 0 10px;letter-spacing:-.01em}
.prose ul,.prose ol{padding-left:20px;margin-bottom:16px}
.prose li{font-size:.9rem;color:var(--body);margin-bottom:7px;line-height:1.75}
.prose strong{color:var(--text);font-weight:600}
.prose code{font-family:'JetBrains Mono',monospace;font-size:.82em;background:var(--border);color:var(--orange);padding:1px 6px;border-radius:3px}

/* KEYBOARD SHORTCUT */
kbd{display:inline-flex;align-items:center;gap:3px;font-family:'JetBrains Mono',monospace;font-size:.78rem;font-weight:700;background:var(--kbd-bg);color:var(--text);border:1px solid var(--kbd-border);border-bottom:2px solid var(--kbd-border);border-radius:4px;padding:2px 7px;white-space:nowrap;margin:0 1px}

/* SHORTCUT TABLE */
.shortcut-grid{display:grid;grid-template-columns:1fr 1fr;gap:10px;margin:16px 0;max-width:740px}
@media(max-width:700px){.shortcut-grid{grid-template-columns:1fr}}
.shortcut-row{background:var(--card);border:1px solid var(--border);border-radius:7px;padding:12px 14px;display:flex;align-items:center;justify-content:space-between;gap:10px}
.shortcut-desc{font-size:.87rem;color:var(--body)}
.shortcut-keys{display:flex;gap:4px;align-items:center;flex-shrink:0}

/* PANEL MOCKUP */
.panel-mock{background:#1e1f22;border:1px solid var(--border);border-radius:8px;overflow:hidden;margin:18px 0;max-width:740px}
.panel-mock-header{background:#2b2d30;border-bottom:1px solid var(--border);padding:8px 14px;font-family:'JetBrains Mono',monospace;font-size:11px;color:var(--muted);display:flex;align-items:center;gap:8px}
.panel-mock-header::before{content:'';width:8px;height:8px;background:var(--ij);border-radius:50%}
.panel-mock-body{padding:16px 18px;font-family:'JetBrains Mono',monospace;font-size:.82rem;line-height:2}
.pm-dir{color:var(--ij)}
.pm-file{color:var(--text)}
.pm-selected{background:rgba(77,140,205,0.18);display:inline-block;width:100%;margin:0 -18px;padding:0 18px}
.pm-kw{color:var(--purple)}
.pm-cl{color:var(--yellow)}
.pm-fn{color:var(--ij)}
.pm-str{color:var(--green)}
.pm-cm{color:var(--muted);font-style:italic}
.pm-num{color:var(--orange)}
.pm-ann{color:var(--yellow)}

/* STEP LIST */
.steps{display:flex;flex-direction:column;gap:0;margin:18px 0;max-width:740px}
.step{display:flex;gap:14px;padding:14px 0;border-bottom:1px solid var(--border)}
.step:last-child{border-bottom:none}
.step-num{width:26px;height:26px;border-radius:50%;background:var(--ij);color:#fff;font-family:'JetBrains Mono',monospace;font-size:11px;font-weight:700;display:flex;align-items:center;justify-content:center;flex-shrink:0;margin-top:2px}
.step-body h4{font-size:.91rem;font-weight:700;color:var(--text);margin-bottom:4px}
.step-body p{font-size:.86rem;color:var(--body);line-height:1.65;margin:0}
.step-body code{font-family:'JetBrains Mono',monospace;font-size:.82em;color:var(--orange)}

/* CALLOUT */
.callout{display:flex;gap:13px;padding:14px 16px;border-radius:7px;margin:18px 0;font-size:.9rem;line-height:1.75;max-width:740px}
.callout-ico{font-size:16px;flex-shrink:0;margin-top:1px}
.callout-body{flex:1}
.callout-body strong{display:block;font-size:.88rem;margin-bottom:3px;font-family:'JetBrains Mono',monospace}
.callout-body p{color:var(--muted);margin:0;font-size:.86rem}
.callout.tip{background:var(--ij-dim);border:1px solid var(--ij-border)}
.callout.tip strong{color:var(--ij)}
.callout.warn{background:var(--yellow-dim);border:1px solid var(--yellow-border)}
.callout.warn strong{color:var(--yellow)}
.callout.good{background:var(--green-dim);border:1px solid var(--green-border)}
.callout.good strong{color:var(--green)}
.callout.danger{background:var(--red-dim);border:1px solid var(--red-border)}
.callout.danger strong{color:var(--red)}

/* TABLE */
.tbl{width:100%;max-width:740px;border-collapse:collapse;margin:14px 0;font-size:.87rem}
.tbl th{text-align:left;padding:8px 12px;font-size:10px;font-weight:700;letter-spacing:.1em;text-transform:uppercase;color:var(--muted);border-bottom:1px solid var(--border2);background:var(--surface)}
.tbl td{padding:9px 12px;border-bottom:1px solid var(--border);color:var(--body);vertical-align:top}
.tbl td:first-child{font-family:'JetBrains Mono',monospace;font-size:.82rem;color:var(--ij);font-weight:500}
.tbl tr:last-child td{border-bottom:none}
.tbl tr:hover td{background:var(--ij-light)}

/* QUIZ */
.quiz{background:var(--card);border:1px solid var(--border);border-radius:8px;padding:22px;margin:28px 0;max-width:740px}
.quiz-label{font-family:'JetBrains Mono',monospace;font-size:9px;font-weight:700;letter-spacing:.14em;text-transform:uppercase;color:var(--ij);margin-bottom:11px}
.quiz-q{font-size:.92rem;font-weight:600;color:var(--text);margin-bottom:16px;line-height:1.55}
.quiz-opts{display:flex;flex-direction:column;gap:8px}
.quiz-opt{background:var(--surface);border:1px solid var(--border2);border-radius:5px;padding:10px 14px;cursor:pointer;font-family:'Inter',sans-serif;font-size:.87rem;color:var(--muted);text-align:left;transition:all .12s}
.quiz-opt:hover:not(:disabled){border-color:var(--ij);color:var(--text);background:var(--ij-light)}
.quiz-opt.correct{border-color:var(--green);color:var(--green);background:var(--green-dim)}
.quiz-opt.wrong{border-color:var(--red);color:var(--red);background:var(--red-dim)}
.quiz-opt:disabled{cursor:default}
.quiz-fb{margin-top:12px;padding:10px 14px;border-radius:5px;font-size:.86rem;font-weight:600;font-family:'JetBrains Mono',monospace;display:none}
.quiz-fb.show{display:block}
.quiz-fb.ok{background:var(--green-dim);color:var(--green);border:1px solid var(--green-border)}
.quiz-fb.bad{background:var(--red-dim);color:var(--red);border:1px solid var(--red-border)}

/* CHALLENGE */
.challenge{background:var(--ij-light);border:1px solid var(--ij-border);border-radius:8px;padding:20px 22px;margin:24px 0;max-width:740px;position:relative;overflow:hidden}
.challenge::before{content:'';position:absolute;top:0;left:0;right:0;height:2px;background:var(--ij)}
.ch-label{font-family:'JetBrains Mono',monospace;font-size:9px;font-weight:700;letter-spacing:.14em;text-transform:uppercase;color:var(--ij);margin-bottom:10px}
.challenge h4{font-size:.93rem;font-weight:700;color:var(--text);margin-bottom:8px}
.challenge p{font-size:.88rem;color:var(--body);line-height:1.75;margin-bottom:8px}
.challenge ul{padding-left:16px}
.challenge li{font-size:.86rem;color:var(--body);margin-bottom:5px;line-height:1.65}
.challenge code{font-family:'JetBrains Mono',monospace;font-size:.82em;color:var(--ij)}

/* NAV */
.lesson-nav{display:flex;justify-content:space-between;align-items:center;margin-top:50px;padding-top:22px;border-top:1px solid var(--border);max-width:740px}
.btn{font-family:'Inter',sans-serif;font-size:12px;font-weight:700;padding:9px 20px;border-radius:5px;cursor:pointer;border:none;transition:all .15s;letter-spacing:.02em}
.btn-next{background:var(--ij);color:#fff}
.btn-next:hover:not(:disabled){background:#3d7abf;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(--ij)}
.btn:disabled{opacity:.3;cursor:not-allowed;transform:none!important}

/* INTERACTIVE SHORTCUT TRAINER */
.shortcut-trainer{background:var(--card);border:1px solid var(--border);border-radius:8px;padding:20px;margin:18px 0;max-width:740px}
.st-label{font-family:'JetBrains Mono',monospace;font-size:9px;font-weight:700;letter-spacing:.14em;text-transform:uppercase;color:var(--ij);margin-bottom:14px}
.st-card{background:#1e1f22;border-radius:7px;padding:18px;text-align:center;margin-bottom:14px}
.st-action{font-size:1rem;font-weight:600;color:var(--text);margin-bottom:6px}
.st-hint{font-size:.83rem;color:var(--muted);margin-bottom:14px}
.st-opts{display:flex;gap:8px;flex-wrap:wrap;justify-content:center}
.st-opt{font-family:'JetBrains Mono',monospace;font-size:.82rem;padding:8px 14px;border:1px solid var(--border2);border-radius:5px;background:var(--surface);color:var(--body);cursor:pointer;transition:all .12s}
.st-opt:hover:not(:disabled){border-color:var(--ij);color:var(--text)}
.st-opt.correct{border-color:var(--green);color:var(--green);background:var(--green-dim)}
.st-opt.wrong{border-color:var(--red);color:var(--red);background:var(--red-dim)}
.st-progress{font-size:.83rem;color:var(--muted);text-align:center}

::-webkit-scrollbar{width:4px;height:4px}
::-webkit-scrollbar-thumb{background:var(--border2);border-radius:2px}
@media(max-width:860px){.sidebar{display:none}.main{padding:28px 20px 60px}header{padding:0 10px}.hdr-tabs{display:none}}
/* 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;
    }
}