:root{--bg-app: #f9f9f9;--bg-card: #ffffff;--bg-card-hover: #fcfcfc;--bg-element: #f0f0f0;--bg-element-active: #e2e2e2;--text-primary: #111111;--text-secondary: #555555;--text-muted: #888888;--text-inverse: #ffffff;--border-light: #e5e5e5;--border-medium: #888888;--border-dark: #111111;--shadow-sm: 0 1px 2px rgba(0, 0, 0, .05);--shadow-md: 0 4px 12px rgba(0, 0, 0, .05);--shadow-lg: 0 12px 24px rgba(0, 0, 0, .08);--font-family: Helvetica, "Helvetica Neue", Arial, sans-serif;--transition-fast: .2s cubic-bezier(.16, 1, .3, 1);--transition-normal: .3s cubic-bezier(.16, 1, .3, 1)}@media (prefers-color-scheme: dark){:root{--bg-app: #121212;--bg-card: #1c1c1e;--bg-card-hover: #242426;--bg-element: #2c2c2e;--bg-element-active: #3a3a3c;--text-primary: #f5f5f7;--text-secondary: #a1a1a6;--text-muted: #636366;--text-inverse: #111111;--border-light: #2c2c2e;--border-medium: #636366;--border-dark: #f5f5f7;--shadow-sm: 0 1px 2px rgba(0, 0, 0, .3);--shadow-md: 0 4px 12px rgba(0, 0, 0, .3);--shadow-lg: 0 12px 24px rgba(0, 0, 0, .4)}}*{box-sizing:border-box;margin:0;padding:0}body{font-family:var(--font-family);background-color:var(--bg-app);color:var(--text-primary);line-height:1.6;-webkit-font-smoothing:antialiased;-moz-osx-font-smoothing:grayscale}.app-container{display:flex;min-height:100vh}.sidebar{width:240px;background-color:var(--bg-card);border-right:1px solid var(--border-light);padding:2rem 1.5rem;display:flex;flex-direction:column;position:fixed;top:0;bottom:0;left:0;overflow-y:auto;z-index:10;transition:transform var(--transition-normal)}.main-content{flex:1;margin-left:240px;padding:3rem;max-width:1000px;margin-right:auto;transition:margin-left var(--transition-normal)}body.sidebar-collapsed .sidebar{transform:translate(-240px)}body.sidebar-collapsed .main-content{margin-left:0}.mobile-header{display:none;background-color:var(--bg-card);border-bottom:1px solid var(--border-light);padding:1rem 1.5rem;position:sticky;top:0;z-index:20;justify-content:space-between;align-items:center}h1,h2,h3,h4,h5,h6{font-weight:700;color:var(--text-primary);letter-spacing:-.02em}h1{font-size:2.5rem;margin-bottom:1.5rem;line-height:1.15}h2{font-size:1.75rem;margin-bottom:1.25rem;line-height:1.25}h3{font-size:1.25rem;margin-bottom:1rem}p{color:var(--text-secondary);margin-bottom:1.5rem;font-size:1.05rem}.btn{display:inline-flex;align-items:center;justify-content:center;padding:.75rem 1.5rem;font-family:var(--font-family);font-size:.95rem;font-weight:600;border-radius:4px;border:1px solid var(--border-dark);cursor:pointer;transition:all var(--transition-fast);text-decoration:none}.btn-primary{background-color:var(--text-primary);color:var(--bg-card)}.btn-primary:hover{background-color:var(--bg-app);color:var(--text-primary)}.btn-secondary{background-color:transparent;color:var(--text-primary);border-color:var(--border-light)}.btn-secondary:hover{background-color:var(--bg-element);border-color:var(--border-medium)}.btn-outline{border:1px solid var(--border-light);background-color:transparent;color:var(--text-secondary)}.btn-outline:hover{border-color:var(--border-medium);color:var(--text-primary)}.btn-disabled{border-color:var(--border-light);background-color:var(--bg-element);color:var(--text-muted);cursor:not-allowed}.card{background-color:var(--bg-card);border:1px solid var(--border-light);border-radius:6px;padding:2rem;margin-bottom:2rem;box-shadow:var(--shadow-sm);transition:border-color var(--transition-fast),box-shadow var(--transition-fast)}.card:hover{border-color:var(--border-medium);box-shadow:var(--shadow-md)}.card-title{margin-bottom:.5rem}.card-meta{font-size:.85rem;text-transform:uppercase;letter-spacing:.05em;color:var(--text-muted);margin-bottom:1rem}.step-container{display:flex;flex-direction:column;gap:1.5rem;margin-top:2rem}.step-item{opacity:0;transform:translateY(15px);animation:slideIn var(--transition-normal) forwards;background-color:var(--bg-card);border-left:3px solid var(--border-dark);padding:1.5rem;border-radius:0 6px 6px 0;box-shadow:var(--shadow-sm)}@keyframes slideIn{to{opacity:1;transform:translateY(0)}}.step-quote{font-style:italic;border-left:2px solid var(--border-medium);padding-left:1rem;margin:1rem 0;color:var(--text-primary)}.form-group{margin-bottom:1.5rem}.form-label{display:block;font-weight:600;font-size:.9rem;margin-bottom:.5rem;color:var(--text-primary)}.text-input{width:100%;padding:.85rem 1rem;font-family:var(--font-family);font-size:1rem;background-color:var(--bg-app);border:1px solid var(--border-light);border-radius:4px;color:var(--text-primary);transition:border-color var(--transition-fast)}.text-input:focus{outline:none;border-color:var(--border-dark)}.quiz-options{display:flex;flex-direction:column;gap:.75rem;margin-top:1rem}.quiz-option{display:flex;align-items:center;padding:1rem;border:1px solid var(--border-light);border-radius:4px;cursor:pointer;transition:all var(--transition-fast);background-color:var(--bg-card)}.quiz-option:hover{background-color:var(--bg-app);border-color:var(--border-medium)}.quiz-option.selected{border-color:var(--border-dark);font-weight:600}.quiz-option.correct{border-left:4px solid var(--text-primary);background-color:var(--bg-element)}.quiz-option.incorrect{border-left:4px solid var(--border-medium);opacity:.7}.quiz-feedback{margin-top:1rem;padding:1rem;background-color:var(--bg-element);border-radius:4px;font-size:.95rem;animation:fadeIn var(--transition-fast) forwards}@keyframes fadeIn{0%{opacity:0}to{opacity:1}}.unit-section{margin-bottom:3.5rem}.unit-header{border-bottom:2px solid var(--border-dark);padding-bottom:.5rem;margin-bottom:1.5rem}.unit-number{font-family:monospace;font-size:.9rem;text-transform:uppercase;color:var(--text-muted)}.lesson-list{display:grid;grid-template-columns:repeat(auto-fill,minmax(280px,1fr));gap:1.5rem}.lesson-card{cursor:pointer}.lesson-card.completed{border-left:4px solid var(--text-primary)}.lesson-card.completed:after{content:" ✓ Đã hoàn thành";font-size:.75rem;font-weight:700;display:block;margin-top:.5rem;color:var(--text-muted)}.progress-container{margin-bottom:2rem}.progress-bar-bg{height:6px;background-color:var(--bg-element);border-radius:3px;overflow:hidden}.progress-bar-fill{height:100%;background-color:var(--text-primary);width:0%;transition:width var(--transition-normal)}.brand{font-weight:800;font-size:1.5rem;margin-bottom:2rem;text-decoration:none;color:var(--text-primary)}.sidebar-nav{list-style:none;display:flex;flex-direction:column;gap:.75rem}.sidebar-link{color:var(--text-secondary);text-decoration:none;font-weight:500;padding:.5rem .75rem;border-radius:4px;transition:all var(--transition-fast)}.sidebar-link:hover,.sidebar-link.active{color:var(--text-primary);background-color:var(--bg-element)}.table-container{width:100%;overflow-x:auto;margin:1.5rem 0}table{width:100%;border-collapse:collapse;text-align:left}th,td{padding:1rem;border-bottom:1px solid var(--border-light)}th{font-weight:700;color:var(--text-primary);border-bottom:2px solid var(--border-dark)}@media (max-width: 768px){.app-container{flex-direction:column}.sidebar{display:none}.main-content{margin-left:0;padding:1.5rem}.mobile-header{display:flex}h1{font-size:2rem}}