/* ═══════════════════════════════════════════
   Linux Mastery — Design System
   ═══════════════════════════════════════════ */
:root {
  --bg-primary: #0a0c14;
  --bg-secondary: #0f1320;
  --bg-card: #151a2e;
  --bg-card-hover: #1b2240;
  --bg-sidebar: #0b0e1a;
  --bg-terminal: #0c0e14;
  --linux-orange: #e95420;
  --linux-orange-light: #ff7043;
  --linux-orange-dark: #c43e10;
  --accent-cyan: #06d6a0;
  --accent-orange: #ff8c42;
  --accent-purple: #a78bfa;
  --accent-pink: #f472b6;
  --accent-red: #ef4444;
  --accent-yellow: #fbbf24;
  --accent-green: #34d399;
  --accent-teal: #2dd4bf;
  --accent-blue: #60a5fa;
  --text-primary: #f1f5f9;
  --text-secondary: #94a3b8;
  --text-muted: #64748b;
  --border-color: rgba(148,163,184,0.08);
  --border-glow: rgba(233,84,32,0.3);
  --sidebar-width: 280px;
  --font-sans: 'Inter', -apple-system, sans-serif;
  --font-mono: 'JetBrains Mono', 'Fira Code', monospace;
  --shadow-md: 0 4px 20px rgba(0,0,0,0.4);
  --shadow-lg: 0 8px 40px rgba(0,0,0,0.5);
  --shadow-glow: 0 0 30px rgba(233,84,32,0.12);
  --transition: 0.25s cubic-bezier(0.4,0,0.2,1);
}
*,*::before,*::after{margin:0;padding:0;box-sizing:border-box}
html{scroll-behavior:smooth}
body{font-family:var(--font-sans);background:var(--bg-primary);color:var(--text-primary);line-height:1.7;overflow:hidden;height:100vh}
#app{display:flex;height:100vh;overflow:hidden}
#sidebar{width:var(--sidebar-width);min-width:var(--sidebar-width);background:var(--bg-sidebar);border-right:1px solid var(--border-color);display:flex;flex-direction:column;overflow-y:auto;transition:transform var(--transition);z-index:100}
.sidebar-header{padding:24px 20px 16px;border-bottom:1px solid var(--border-color)}
.logo{display:flex;align-items:center;gap:10px;margin-bottom:16px}
.logo-icon{font-size:28px;animation:float 3s ease-in-out infinite}
@keyframes float{0%,100%{transform:translateY(0)}50%{transform:translateY(-4px)}}
.logo-text{font-size:20px;font-weight:800;background:linear-gradient(135deg,var(--linux-orange),var(--accent-yellow));-webkit-background-clip:text;background-clip:text;-webkit-text-fill-color:transparent;letter-spacing:-0.3px}
.progress-bar-container{width:100%;height:6px;background:rgba(255,255,255,0.06);border-radius:10px;overflow:hidden}
.progress-bar{height:100%;width:0%;background:linear-gradient(90deg,var(--linux-orange),var(--accent-yellow));border-radius:10px;transition:width 0.5s ease}
.progress-label{display:block;margin-top:8px;font-size:12px;color:var(--text-muted);font-weight:500}
.nav-list{list-style:none;flex:1;overflow-y:auto;padding:12px 10px}
.nav-item{margin-bottom:2px}
.nav-link{display:flex;align-items:center;gap:10px;padding:10px 14px;border-radius:10px;cursor:pointer;color:var(--text-secondary);font-size:13.5px;font-weight:500;transition:all var(--transition);user-select:none;position:relative}
.nav-link:hover{background:rgba(255,255,255,0.04);color:var(--text-primary)}
.nav-link.active{background:rgba(233,84,32,0.12);color:var(--linux-orange-light);font-weight:600}
.nav-link.active::before{content:'';position:absolute;left:0;top:50%;transform:translateY(-50%);width:3px;height:60%;background:var(--linux-orange);border-radius:0 4px 4px 0}
.nav-link.completed{color:var(--accent-green)}
.nav-icon{font-size:16px;width:24px;text-align:center;flex-shrink:0}
.nav-check{margin-left:auto;font-size:14px;opacity:0;transition:opacity var(--transition)}
.nav-link.completed .nav-check{opacity:1}
.nav-section-title{padding:16px 14px 6px;font-size:10px;text-transform:uppercase;letter-spacing:1.5px;color:var(--text-muted);font-weight:700}
.sidebar-footer{padding:12px 14px;border-top:1px solid var(--border-color)}
.btn-reset{width:100%;padding:8px;background:transparent;border:1px solid var(--border-color);color:var(--text-muted);border-radius:8px;font-family:var(--font-sans);font-size:12px;cursor:pointer;transition:all var(--transition)}
.btn-reset:hover{border-color:var(--accent-red);color:var(--accent-red);background:rgba(239,68,68,0.08)}
#mainContent{flex:1;display:flex;flex-direction:column;overflow:hidden}
.topbar{display:none;align-items:center;gap:12px;padding:12px 20px;background:var(--bg-secondary);border-bottom:1px solid var(--border-color)}
.btn-menu{background:none;border:none;color:var(--text-primary);font-size:22px;cursor:pointer;padding:4px}
.topbar-title{font-size:14px;font-weight:600;color:var(--text-secondary)}
.lesson-container{flex:1;overflow-y:auto;padding:40px;scroll-behavior:smooth}
.lesson-nav{display:flex;justify-content:space-between;padding:16px 40px;border-top:1px solid var(--border-color);background:var(--bg-secondary)}
.btn{padding:10px 24px;border-radius:10px;border:none;font-family:var(--font-sans);font-size:14px;font-weight:600;cursor:pointer;transition:all var(--transition);display:flex;align-items:center;gap:6px}
.btn-prev{background:var(--bg-card);color:var(--text-secondary);border:1px solid var(--border-color)}
.btn-prev:hover{background:var(--bg-card-hover);color:var(--text-primary)}
.btn-next{background:linear-gradient(135deg,var(--linux-orange),var(--linux-orange-dark));color:white;box-shadow:0 4px 15px rgba(233,84,32,0.3)}
.btn-next:hover{transform:translateY(-1px);box-shadow:0 6px 20px rgba(233,84,32,0.4)}
.btn:disabled{opacity:0.3;cursor:not-allowed;transform:none!important}
.lesson{max-width:860px;margin:0 auto;animation:fadeIn 0.4s ease}
@keyframes fadeIn{from{opacity:0;transform:translateY(12px)}to{opacity:1;transform:translateY(0)}}
.lesson-badge{display:inline-flex;align-items:center;gap:6px;padding:5px 14px;background:rgba(233,84,32,0.1);border:1px solid rgba(233,84,32,0.2);border-radius:20px;font-size:12px;font-weight:600;color:var(--linux-orange-light);margin-bottom:16px;text-transform:uppercase;letter-spacing:0.5px}
.lesson h1{font-size:36px;font-weight:900;line-height:1.2;margin-bottom:12px;letter-spacing:-0.5px}
.lesson h1 .emoji{margin-right:10px}
.lesson-subtitle{font-size:17px;color:var(--text-secondary);line-height:1.6;margin-bottom:36px}
.lesson h2{font-size:22px;font-weight:700;margin:36px 0 16px;color:var(--text-primary);display:flex;align-items:center;gap:10px}
.lesson h3{font-size:17px;font-weight:700;margin:24px 0 10px;color:var(--text-primary)}
.lesson p{margin-bottom:16px;color:var(--text-secondary);font-size:15px;line-height:1.8}
.lesson ul,.lesson ol{margin:0 0 16px 20px;color:var(--text-secondary)}
.lesson li{margin-bottom:8px;font-size:15px;line-height:1.7}
.visual-box{background:var(--bg-card);border:1px solid var(--border-color);border-radius:16px;padding:28px;margin:24px 0;position:relative;overflow:hidden}
.visual-box::before{content:'';position:absolute;top:0;left:0;right:0;height:2px;background:linear-gradient(90deg,var(--linux-orange),var(--accent-yellow),var(--accent-cyan))}
.visual-box.green::before{background:linear-gradient(90deg,var(--accent-green),var(--accent-cyan))}
.visual-box.orange::before{background:linear-gradient(90deg,var(--accent-orange),var(--accent-yellow))}
.visual-box.purple::before{background:linear-gradient(90deg,var(--accent-purple),var(--accent-pink))}
.analogy-box{background:linear-gradient(135deg,rgba(233,84,32,0.08),rgba(251,191,36,0.05));border:1px solid rgba(233,84,32,0.15);border-radius:14px;padding:24px;margin:24px 0}
.analogy-box .analogy-emoji{font-size:36px;margin-bottom:12px;display:block}
.analogy-box .analogy-title{font-size:14px;font-weight:700;color:var(--linux-orange-light);text-transform:uppercase;letter-spacing:1px;margin-bottom:8px}
.analogy-box p{color:var(--text-primary);font-size:15px}
.terminal{background:var(--bg-terminal);border:1px solid rgba(255,255,255,0.06);border-radius:12px;margin:20px 0;overflow:hidden;box-shadow:var(--shadow-md)}
.terminal-header{display:flex;align-items:center;gap:8px;padding:10px 16px;background:rgba(255,255,255,0.03);border-bottom:1px solid rgba(255,255,255,0.04)}
.terminal-dot{width:10px;height:10px;border-radius:50%}
.terminal-dot.red{background:#ff5f57}.terminal-dot.yellow{background:#febc2e}.terminal-dot.green{background:#28c840}
.terminal-title{margin-left:8px;font-size:12px;color:var(--text-muted);font-family:var(--font-mono)}
.terminal-body{padding:18px 20px;overflow-x:auto}
.terminal-body code{font-family:var(--font-mono);font-size:13.5px;line-height:1.8;color:#e2e8f0;white-space:pre;display:block}
.terminal-body .comment{color:#64748b}.terminal-body .command{color:var(--accent-cyan)}.terminal-body .flag{color:var(--accent-orange)}.terminal-body .string{color:var(--accent-yellow)}.terminal-body .output{color:var(--text-muted)}.terminal-body .keyword{color:var(--accent-purple)}.terminal-body .success{color:var(--accent-green)}.terminal-body .err{color:var(--accent-red)}
.inline-code{font-family:var(--font-mono);font-size:13px;background:rgba(233,84,32,0.12);color:var(--linux-orange-light);padding:2px 8px;border-radius:5px;border:1px solid rgba(233,84,32,0.15)}
.diagram{background:var(--bg-card);border:1px solid var(--border-color);border-radius:14px;padding:30px;margin:24px 0;display:flex;flex-direction:column;align-items:center;gap:16px;overflow-x:auto}
.diagram-title{font-size:13px;font-weight:700;text-transform:uppercase;letter-spacing:1.5px;color:var(--text-muted);margin-bottom:8px}
.diagram-row{display:flex;align-items:center;gap:12px;flex-wrap:wrap;justify-content:center}
.diagram-box{display:flex;flex-direction:column;align-items:center;gap:6px;padding:16px 20px;border-radius:12px;font-size:13px;font-weight:600;min-width:100px;text-align:center;transition:transform 0.3s ease}
.diagram-box:hover{transform:translateY(-3px)}
.diagram-box.orange{background:rgba(233,84,32,0.15);border:1px solid rgba(233,84,32,0.3);color:var(--linux-orange-light)}
.diagram-box.blue{background:rgba(96,165,250,0.12);border:1px solid rgba(96,165,250,0.25);color:var(--accent-blue)}
.diagram-box.green{background:rgba(6,214,160,0.12);border:1px solid rgba(6,214,160,0.25);color:var(--accent-green)}
.diagram-box.purple{background:rgba(167,139,250,0.12);border:1px solid rgba(167,139,250,0.25);color:var(--accent-purple)}
.diagram-box.pink{background:rgba(244,114,182,0.12);border:1px solid rgba(244,114,182,0.25);color:var(--accent-pink)}
.diagram-box.teal{background:rgba(45,212,191,0.12);border:1px solid rgba(45,212,191,0.25);color:var(--accent-teal)}
.diagram-box.yellow{background:rgba(251,191,36,0.12);border:1px solid rgba(251,191,36,0.25);color:var(--accent-yellow)}
.diagram-box .box-icon{font-size:24px}
.diagram-arrow{font-size:20px;color:var(--text-muted)}
.compare-table{width:100%;border-collapse:separate;border-spacing:0;margin:20px 0;border-radius:12px;overflow:hidden;border:1px solid var(--border-color)}
.compare-table th{background:rgba(233,84,32,0.1);color:var(--linux-orange-light);padding:14px 18px;font-size:13px;font-weight:700;text-transform:uppercase;letter-spacing:0.5px;text-align:left}
.compare-table td{padding:12px 18px;font-size:14px;color:var(--text-secondary);border-bottom:1px solid var(--border-color);background:var(--bg-card)}
.compare-table tr:last-child td{border-bottom:none}
.compare-table tr:hover td{background:var(--bg-card-hover)}
.quiz{background:var(--bg-card);border:1px solid var(--border-color);border-radius:14px;padding:28px;margin:28px 0}
.quiz-title{font-size:16px;font-weight:700;margin-bottom:4px;display:flex;align-items:center;gap:8px}
.quiz-question{color:var(--text-secondary);font-size:15px;margin-bottom:16px}
.quiz-options{display:flex;flex-direction:column;gap:8px}
.quiz-option{display:flex;align-items:center;gap:12px;padding:12px 16px;border-radius:10px;border:1px solid var(--border-color);cursor:pointer;transition:all var(--transition);font-size:14px;color:var(--text-secondary)}
.quiz-option:hover{border-color:var(--linux-orange);background:rgba(233,84,32,0.06);color:var(--text-primary)}
.quiz-option.selected{border-color:var(--linux-orange);background:rgba(233,84,32,0.1);color:var(--text-primary)}
.quiz-option.correct{border-color:var(--accent-green);background:rgba(6,214,160,0.1);color:var(--accent-green)}
.quiz-option.wrong{border-color:var(--accent-red);background:rgba(239,68,68,0.1);color:var(--accent-red)}
.quiz-option .option-letter{width:26px;height:26px;display:flex;align-items:center;justify-content:center;border-radius:7px;background:rgba(255,255,255,0.04);font-weight:700;font-size:12px;flex-shrink:0}
.quiz-feedback{margin-top:14px;padding:12px 16px;border-radius:10px;font-size:14px;display:none}
.quiz-feedback.show{display:block}
.quiz-feedback.correct{background:rgba(6,214,160,0.08);border:1px solid rgba(6,214,160,0.2);color:var(--accent-green)}
.quiz-feedback.wrong{background:rgba(239,68,68,0.08);border:1px solid rgba(239,68,68,0.2);color:var(--accent-red)}
.callout{padding:18px 20px;border-radius:12px;margin:20px 0;font-size:14px;line-height:1.7;display:flex;gap:12px}
.callout-icon{font-size:20px;flex-shrink:0;margin-top:2px}
.callout.tip{background:rgba(6,214,160,0.06);border:1px solid rgba(6,214,160,0.15);color:var(--accent-green)}
.callout.warn{background:rgba(251,191,36,0.06);border:1px solid rgba(251,191,36,0.15);color:var(--accent-yellow)}
.callout.info{background:rgba(96,165,250,0.06);border:1px solid rgba(96,165,250,0.15);color:var(--accent-blue)}
.callout.danger{background:rgba(239,68,68,0.06);border:1px solid rgba(239,68,68,0.15);color:var(--accent-red)}
.steps{display:flex;flex-direction:column;gap:16px;margin:20px 0}
.step-card{display:flex;gap:16px;padding:20px;background:var(--bg-card);border:1px solid var(--border-color);border-radius:14px;transition:all var(--transition)}
.step-card:hover{border-color:var(--border-glow);box-shadow:var(--shadow-glow)}
.step-number{width:36px;height:36px;display:flex;align-items:center;justify-content:center;border-radius:10px;background:linear-gradient(135deg,var(--linux-orange),var(--linux-orange-dark));color:white;font-weight:800;font-size:14px;flex-shrink:0}
.step-content h4{font-size:15px;font-weight:700;margin-bottom:4px;color:var(--text-primary)}
.step-content p{font-size:14px;color:var(--text-secondary);margin:0}
.hero-card{text-align:center;padding:60px 40px;background:linear-gradient(135deg,rgba(233,84,32,0.08),rgba(251,191,36,0.04),rgba(167,139,250,0.04));border:1px solid rgba(233,84,32,0.15);border-radius:20px;margin-bottom:36px}
.hero-icon{font-size:72px;display:block;margin-bottom:16px;animation:float 3s ease-in-out infinite}
.hero-card h1{font-size:42px;font-weight:900;margin-bottom:12px;background:linear-gradient(135deg,var(--linux-orange-light),var(--accent-yellow));-webkit-background-clip:text;background-clip:text;-webkit-text-fill-color:transparent}
.feature-grid{display:grid;grid-template-columns:repeat(auto-fit,minmax(220px,1fr));gap:16px;margin:24px 0}
.feature-item{padding:24px;background:var(--bg-card);border:1px solid var(--border-color);border-radius:14px;text-align:center;transition:all var(--transition)}
.feature-item:hover{border-color:var(--border-glow);transform:translateY(-3px);box-shadow:var(--shadow-glow)}
.feature-item .fi-icon{font-size:32px;display:block;margin-bottom:12px}
.feature-item .fi-title{font-size:15px;font-weight:700;color:var(--text-primary);margin-bottom:6px}
.feature-item .fi-desc{font-size:13px;color:var(--text-muted);line-height:1.5}
.cheat-grid{display:grid;grid-template-columns:1fr 1fr;gap:12px;margin:20px 0}
.cheat-item{padding:16px;background:var(--bg-card);border:1px solid var(--border-color);border-radius:12px;transition:all var(--transition)}
.cheat-item:hover{border-color:var(--border-glow)}
.cheat-cmd{font-family:var(--font-mono);font-size:13px;color:var(--accent-cyan);margin-bottom:6px;font-weight:600}
.cheat-desc{font-size:12px;color:var(--text-muted);line-height:1.5}
.fs-tree{font-family:var(--font-mono);font-size:13px;line-height:2;color:var(--text-secondary);padding:16px 20px;background:var(--bg-card);border:1px solid var(--border-color);border-radius:12px;margin:20px 0}
.fs-tree .dir{color:var(--accent-blue);font-weight:600}
.fs-tree .file{color:var(--text-secondary)}
.fs-tree .important{color:var(--linux-orange-light);font-weight:600}
.perm-block{font-family:var(--font-mono);font-size:16px;letter-spacing:2px;text-align:center;padding:16px;background:var(--bg-card);border-radius:12px;border:1px solid var(--border-color);margin:16px 0}
.perm-block .perm-r{color:var(--accent-green)}.perm-block .perm-w{color:var(--accent-yellow)}.perm-block .perm-x{color:var(--accent-red)}.perm-block .perm-d{color:var(--accent-blue)}.perm-block .perm-dash{color:var(--text-muted)}
@media(max-width:900px){
  #sidebar{position:fixed;top:0;left:0;height:100vh;transform:translateX(-100%);box-shadow:var(--shadow-lg)}
  #sidebar.open{transform:translateX(0)}
  .topbar{display:flex}.lesson-container{padding:24px 20px}.lesson-nav{padding:12px 20px}
  .hero-card{padding:40px 20px}.hero-card h1{font-size:28px}
  .cheat-grid{grid-template-columns:1fr}.feature-grid{grid-template-columns:1fr}
}
.sidebar-overlay{display:none;position:fixed;top:0;left:0;width:100%;height:100%;background:rgba(0,0,0,0.6);z-index:99;backdrop-filter:blur(4px)}
.sidebar-overlay.show{display:block}
::-webkit-scrollbar{width:6px}::-webkit-scrollbar-track{background:transparent}::-webkit-scrollbar-thumb{background:rgba(255,255,255,0.08);border-radius:10px}::-webkit-scrollbar-thumb:hover{background:rgba(255,255,255,0.15)}