@import"https://fonts.googleapis.com/css2?family=Inter:wght@400;600;700;800&family=Playfair+Display:wght@400;600;700;800&display=swap";:root{--kntt-blue-50: #eff6ff;--kntt-blue-100: #dbeafe;--kntt-blue-200: #bfdbfe;--kntt-blue-400: #60a5fa;--kntt-blue-500: #3b82f6;--kntt-blue-600: #2563eb;--kntt-blue-700: #1d4ed8;--kntt-blue-800: #1e40af;--kntt-blue-900: #1e3a8a;--kntt-teal-400: #2dd4bf;--kntt-teal-500: #14b8a6;--kntt-teal-600: #0d9488;--kntt-green-100: #dcfce7;--kntt-green-500: #22c55e;--kntt-yellow-100: #fef9c3;--kntt-yellow-500: #eab308;--kntt-orange-100: #ffedd5;--kntt-orange-500: #f97316;--kntt-red-100: #fee2e2;--kntt-red-500: #ef4444;--kntt-purple-100: #f3e8ff;--kntt-purple-600: #9333ea;--font-body: "Inter", "Playfair Display", system-ui, -apple-system, sans-serif;--sidebar-w: 260px;--header-h: 64px;--content-max: 880px;--t-fast: .15s ease;--t-medium: .25s ease;--t-slow: .4s ease}*,*:before,*:after{box-sizing:border-box;margin:0;padding:0}html{font-family:var(--font-body);font-size:16px;line-height:1.7;color:#1e293b;background:#f8fafc;scroll-behavior:smooth}body{min-height:100vh}img,svg{display:block;max-width:100%}h1,h2,h3,h4{font-weight:700;line-height:1.3;color:#0f172a}h1{font-size:clamp(1.5rem,4vw,2.1rem)}h2{font-size:clamp(1.2rem,3vw,1.55rem)}h3{font-size:1.1rem}p{margin-bottom:.75rem}p:last-child{margin-bottom:0}strong{font-weight:700;color:var(--kntt-blue-800)}.site-wrapper{display:flex;flex-direction:column;min-height:100vh}.page-body{display:flex;flex:1;position:relative}.main-content-wrapper{flex:1;display:flex;justify-content:center;min-width:0}.content-area{max-width:var(--content-max);padding:2rem 1.5rem 4rem;width:100%}.sidebar{position:sticky;top:var(--header-h);height:calc(100vh - var(--header-h));overflow-y:auto;background:#fff;padding:1.25rem 1rem;flex-shrink:0;scrollbar-width:thin;z-index:40}.left-sidebar{width:var(--sidebar-w);border-right:1px solid #e2e8f0}.right-sidebar{width:240px;border-left:1px solid #e2e8f0;background:#f8fafc}.mobile-menu-btn{display:flex;align-items:center;justify-content:center;background:transparent;border:none;color:#fff;padding:.5rem;cursor:pointer;border-radius:6px;margin-right:.5rem}.mobile-menu-btn:hover{background:#ffffff26}.sidebar-backdrop{display:none;position:fixed;inset:0;top:var(--header-h);background:#0f172a66;z-index:30;opacity:0;transition:opacity var(--t-fast)}.sidebar-backdrop.open{display:block;opacity:1}.toc-container{padding:.5rem 0}.toc-title{font-size:.7rem;font-weight:800;color:var(--kntt-orange-500);letter-spacing:.05em;margin-bottom:1rem}.toc-list{list-style:none;padding-left:.5rem;border-left:2px solid #e2e8f0;display:flex;flex-direction:column;gap:.6rem}.toc-list a{font-size:.85rem;color:var(--kntt-teal-600);font-weight:600;text-decoration:none;transition:color var(--t-fast);display:block;line-height:1.4}.toc-list a:hover{color:var(--kntt-teal-400)}.toc-list a.active{color:var(--kntt-orange-500);font-weight:700;border-left:2px solid var(--kntt-orange-500);padding-left:.4rem;margin-left:-.6rem}.mobile-toc-btn{display:none;position:fixed;top:calc(var(--header-h) + 20px);right:20px;width:50px;height:50px;border-radius:50%;background:var(--kntt-orange-500);color:#fff;border:none;box-shadow:0 4px 12px #f9731666;z-index:50;cursor:pointer;align-items:center;justify-content:center;transition:transform var(--t-fast)}.mobile-toc-btn:active{transform:scale(.95)}.desktop-nav{display:flex;gap:.25rem;margin-left:auto}.site-header{position:sticky;top:0;z-index:100;height:var(--header-h);background:linear-gradient(90deg,#1d4ed8,#1e40af);color:#fff;display:flex;align-items:center;gap:1rem;padding:0 1.5rem;box-shadow:0 2px 12px #0003}.site-header .logo{display:flex;align-items:center;gap:.6rem;font-size:1.2rem;font-weight:800;color:#fff;text-decoration:none}.site-header nav{display:none}.site-header nav a{color:#ffffffd9;text-decoration:none;padding:.4rem .85rem;border-radius:8px;font-size:.875rem;font-weight:500;transition:background var(--t-fast)}.site-header nav a:hover,.site-header nav a.active{background:#ffffff2e;color:#fff}.sidebar{position:sticky;top:var(--header-h);height:calc(100vh - var(--header-h));overflow-y:auto;background:#fff;border-right:1px solid #e2e8f0;padding:1.25rem 1rem}.sidebar-title{font-size:.7rem;font-weight:700;text-transform:uppercase;letter-spacing:.1em;color:#94a3b8;margin-bottom:.75rem;padding:0 .5rem}.sidebar-lesson-list{list-style:none;display:flex;flex-direction:column;gap:.15rem}.sidebar-lesson-list a{display:flex;align-items:center;gap:.5rem;padding:.5rem .75rem;border-radius:8px;text-decoration:none;color:var(--kntt-blue-600);font-size:.875rem;transition:all var(--t-fast);line-height:1.4;cursor:pointer}.sidebar-lesson-list a:hover{background:var(--kntt-blue-50);color:var(--kntt-blue-700)}.sidebar-lesson-list a.active{background:var(--kntt-blue-100);color:var(--kntt-blue-800);font-weight:700}.sidebar-lesson-list a.lesson-coming-soon{color:var(--kntt-blue-600);opacity:.72;position:relative}.sidebar-lesson-list a.lesson-coming-soon:after{content:"✏";font-size:.65rem;opacity:.55;margin-left:auto;flex-shrink:0}.sidebar-lesson-list a.lesson-coming-soon:hover{background:var(--kntt-blue-50);color:var(--kntt-blue-700);opacity:.9}.sidebar-grade-tag{font-size:.7rem;font-weight:700;padding:.1rem .4rem;border-radius:4px;background:var(--kntt-blue-100);color:var(--kntt-blue-700);flex-shrink:0}.lesson-section{border-radius:16px;padding:1.5rem 1.75rem;margin-bottom:1.75rem;position:relative;overflow:hidden}.section-badge{display:inline-flex;align-items:center;gap:.4rem;font-size:.75rem;font-weight:700;text-transform:uppercase;letter-spacing:.08em;padding:.25rem .7rem;border-radius:20px;margin-bottom:.75rem}.section-khoi-dong{background:linear-gradient(135deg,#eff6ff,#dbeafe);border:2px solid var(--kntt-blue-200)}.section-khoi-dong .section-badge{background:var(--kntt-blue-600);color:#fff}.section-khoi-dong h2,.section-khoi-dong h3{color:var(--kntt-blue-800)}.section-kham-pha{background:linear-gradient(135deg,#f0fdfa,#ccfbf1);border:2px solid #99f6e4}.section-kham-pha .section-badge{background:var(--kntt-teal-600);color:#fff}.section-kham-pha h2,.section-kham-pha h3{color:#0f766e}.section-luyen-tap{background:linear-gradient(135deg,#faf5ff,#f3e8ff);border:2px solid #e9d5ff}.section-luyen-tap .section-badge{background:var(--kntt-purple-600);color:#fff}.section-luyen-tap h2,.section-luyen-tap h3{color:#7e22ce}.section-van-dung{background:linear-gradient(135deg,#fff7ed,#ffedd5);border:2px solid #fed7aa}.section-van-dung .section-badge{background:var(--kntt-orange-500);color:#fff}.section-van-dung h2,.section-van-dung h3{color:#c2410c}.section-ghi-nho{background:linear-gradient(135deg,#fefce8,#fef9c3);border:2px solid #fde047;border-left:5px solid var(--kntt-yellow-500)}.section-ghi-nho .section-badge{background:var(--kntt-yellow-500);color:#713f12}.section-ghi-nho h2,.section-ghi-nho h3{color:#713f12}.box-dinh-nghia,.box-dinh-ly,.box-nhan-xet{background:#fff;border-radius:12px;padding:1.25rem 1.5rem;margin:1rem 0;position:relative}.box-dinh-nghia{border:2px solid #93c5fd}.box-dinh-nghia:before{content:"Định nghĩa";position:absolute;top:-12px;left:16px;background:var(--kntt-blue-600);color:#fff;font-size:.72rem;font-weight:700;padding:.2rem .6rem;border-radius:6px;letter-spacing:.05em;text-transform:uppercase}.box-dinh-ly{border:2px solid #99f6e4}.box-dinh-ly:before{content:"Định lý";position:absolute;top:-12px;left:16px;background:var(--kntt-teal-600);color:#fff;font-size:.72rem;font-weight:700;padding:.2rem .6rem;border-radius:6px;letter-spacing:.05em;text-transform:uppercase}.box-nhan-xet{border:2px solid #e9d5ff}.box-nhan-xet:before{content:"Nhận xét";position:absolute;top:-12px;left:16px;background:var(--kntt-purple-600);color:#fff;font-size:.72rem;font-weight:700;padding:.2rem .6rem;border-radius:6px;letter-spacing:.05em;text-transform:uppercase}.katex-display{margin:1rem 0;overflow-x:auto;padding:.5rem 0}.katex{font-size:1.05em}.katex .text{font-family:var(--font-body)!important}.btn{display:inline-flex;align-items:center;gap:.4rem;padding:.55rem 1.2rem;border-radius:8px;font-family:var(--font-body);font-size:.9rem;font-weight:600;cursor:pointer;border:none;transition:all var(--t-fast);text-decoration:none}.btn-primary{background:var(--kntt-blue-600);color:#fff}.btn-primary:hover{background:var(--kntt-blue-700);transform:translateY(-1px)}.btn-secondary{background:#fff;color:var(--kntt-blue-600);border:2px solid var(--kntt-blue-200)}.btn-secondary:hover{background:var(--kntt-blue-50)}.btn-teal{background:var(--kntt-teal-600);color:#fff}.btn-teal:hover{background:var(--kntt-teal-500)}.btn-sm{padding:.35rem .8rem;font-size:.82rem}.quiz-question{font-weight:600;font-size:1rem;margin-bottom:1rem;color:#1e293b}.quiz-options{display:flex;flex-direction:column;gap:.6rem}.quiz-option{display:flex;align-items:center;gap:.75rem;padding:.75rem 1rem;border:2px solid #e2e8f0;border-radius:10px;cursor:pointer;background:#fff;font-family:var(--font-body);font-size:.95rem;text-align:left;transition:all var(--t-fast);width:100%}.quiz-option:hover:not(:disabled){border-color:var(--kntt-blue-400);background:var(--kntt-blue-50)}.quiz-option.correct{border-color:var(--kntt-green-500);background:var(--kntt-green-100);color:#14532d}.quiz-option.incorrect{border-color:var(--kntt-red-500);background:var(--kntt-red-100);color:#7f1d1d}.quiz-option .option-key{width:28px;height:28px;border-radius:50%;background:#e2e8f0;display:flex;align-items:center;justify-content:center;font-weight:700;font-size:.8rem;flex-shrink:0;transition:all var(--t-fast)}.quiz-option:hover:not(:disabled) .option-key{background:var(--kntt-blue-500);color:#fff}.quiz-option.correct .option-key{background:var(--kntt-green-500);color:#fff}.quiz-option.incorrect .option-key{background:var(--kntt-red-500);color:#fff}.msq-checkbox{width:20px;height:20px;border-radius:5px;border:2px solid #94a3b8;background:#fff;display:flex;align-items:center;justify-content:center;font-size:.85rem;font-weight:700;flex-shrink:0;transition:all var(--t-fast);color:#fff}.msq-checked{background:#6366f1;border-color:#6366f1;color:#fff}.quiz-option.correct .msq-checkbox{background:var(--kntt-green-500);border-color:var(--kntt-green-500);color:#fff}.quiz-option.incorrect .msq-checkbox{background:var(--kntt-red-500);border-color:var(--kntt-red-500);color:#fff}.quiz-option:hover:not(:disabled) .msq-checkbox{border-color:#6366f1}.quiz-feedback{margin-top:1rem;padding:.875rem 1rem;border-radius:10px;font-size:.9rem;display:flex;align-items:flex-start;gap:.6rem}.quiz-feedback.correct{background:var(--kntt-green-100);color:#14532d;border:1px solid #bbf7d0}.quiz-feedback.incorrect{background:var(--kntt-red-100);color:#7f1d1d;border:1px solid #fecaca}.jxg-board-wrapper{border-radius:12px;overflow:hidden;border:2px solid #e2e8f0;background:#fff;margin:1rem 0}.jxgbox{touch-action:none}.progress-track{height:6px;background:#e2e8f0;border-radius:99px;overflow:hidden;margin:.5rem 0}.progress-fill{height:100%;background:linear-gradient(90deg,var(--kntt-blue-500),var(--kntt-teal-500));border-radius:99px;transition:width var(--t-slow)}.score-badge{display:inline-flex;align-items:center;gap:.4rem;padding:.3rem .8rem;border-radius:20px;font-weight:700;font-size:.9rem}.score-badge.perfect{background:var(--kntt-green-100);color:#14532d}.score-badge.good{background:var(--kntt-blue-100);color:var(--kntt-blue-800)}.score-badge.fair{background:var(--kntt-yellow-100);color:#713f12}.score-badge.poor{background:var(--kntt-red-100);color:#7f1d1d}.lesson-card{background:#fff;border-radius:16px;border:1px solid #e2e8f0;padding:1.5rem;text-decoration:none;color:inherit;display:flex;flex-direction:column;gap:.75rem;transition:all var(--t-medium);box-shadow:0 1px 3px #0000000f}.lesson-card:hover{box-shadow:0 8px 24px #2563eb1f;transform:translateY(-3px);border-color:var(--kntt-blue-200)}.lesson-card-grade{font-size:.72rem;font-weight:700;text-transform:uppercase;letter-spacing:.08em;padding:.2rem .6rem;border-radius:6px;background:var(--kntt-blue-100);color:var(--kntt-blue-700);align-self:flex-start}.lesson-card-title{font-size:1.05rem;font-weight:700;color:#0f172a;line-height:1.4}.lesson-card-desc{font-size:.875rem;color:#64748b;line-height:1.5}.hero{background:linear-gradient(135deg,#1d4ed8,#1e3a8a 60%,#172554);color:#fff;padding:5rem 2rem;text-align:center;position:relative;overflow:hidden}.hero h1{color:#fff;font-size:clamp(2rem,5vw,3rem);margin-bottom:1rem}.hero p{color:#ffffffd9;font-size:1.1rem;max-width:600px;margin:0 auto 2rem}@keyframes fadeInUp{0%{opacity:0;transform:translateY(20px)}to{opacity:1;transform:translateY(0)}}@keyframes pulse{0%,to{transform:scale(1)}50%{transform:scale(1.05)}}@keyframes draw{to{stroke-dashoffset:0}}@keyframes float{0%,to{transform:translateY(0)}50%{transform:translateY(-10px)}}.animate-fade-in-up{animation:fadeInUp .5s ease forwards}.animate-float{animation:float 3s ease-in-out infinite}.lesson-chapter{font-size:.8rem;font-weight:600;color:var(--kntt-blue-500);text-transform:uppercase;letter-spacing:.08em;margin-bottom:.4rem}.lesson-main-title{font-size:clamp(1.5rem,4vw,2rem);font-weight:800;color:#0f172a;margin-bottom:.5rem}input[type=range]{-webkit-appearance:none;appearance:none;width:100%;height:6px;border-radius:99px;background:#e2e8f0;cursor:pointer}input[type=range]::-webkit-slider-thumb{-webkit-appearance:none;appearance:none;width:20px;height:20px;border-radius:50%;background:var(--kntt-blue-500);border:3px solid white;box-shadow:0 2px 6px #3b82f666;cursor:grab}.lesson-nav{display:flex;justify-content:space-between;gap:1rem;margin-top:3rem;padding-top:2rem;border-top:2px solid #e2e8f0}.lesson-nav a{display:flex;align-items:center;gap:.5rem;padding:.75rem 1.25rem;border-radius:10px;background:#fff;border:2px solid #e2e8f0;text-decoration:none;color:var(--kntt-blue-700);font-weight:600;font-size:.9rem;transition:all var(--t-fast)}.lesson-nav a:hover{background:var(--kntt-blue-50);border-color:var(--kntt-blue-300)}::-webkit-scrollbar{width:6px;height:6px}::-webkit-scrollbar-track{background:transparent}::-webkit-scrollbar-thumb{background:#cbd5e1;border-radius:99px}@media(min-width:901px){.left-sidebar{transition:width var(--t-medium),padding var(--t-medium),opacity var(--t-medium)}.left-sidebar.collapsed{width:0;padding-left:0;padding-right:0;border:none;overflow:hidden;opacity:0}}@media(max-width:1150px){.mobile-toc-btn{display:flex}.right-sidebar{position:fixed;top:var(--header-h);right:-100%;bottom:0;height:calc(100vh - var(--header-h));transition:right var(--t-medium);box-shadow:-4px 0 15px #0000001a;z-index:45;display:block}.right-sidebar.open{right:0}}@media(max-width:900px){.page-body{flex-direction:column}.desktop-nav{display:none}.left-sidebar{position:fixed;top:var(--header-h);left:-100%;bottom:0;transition:left var(--t-medium);box-shadow:4px 0 15px #0000001a;height:calc(100vh - var(--header-h));border-right:none;width:280px}.left-sidebar.open{left:0}}@media(max-width:600px){.lesson-section{padding:1.25rem}.content-area{padding:1rem 1rem 3rem}.hero{padding:3rem 1rem}}.grade-chapter-title{font-weight:700;font-size:1rem;margin-bottom:.6rem;color:var(--kntt-blue-800)}.grade-lesson-list{list-style:none;margin:0;padding:0}.grade-lesson-item{margin-bottom:.35rem}.grade-lesson-link{color:var(--kntt-blue-600);text-decoration:none;font-size:.95rem;font-weight:500;transition:all var(--t-fast);display:inline-flex;align-items:center}.grade-lesson-link:before{content:"•";margin-right:.5rem;color:var(--kntt-blue-400);font-size:1.2rem;line-height:1;transition:all var(--t-fast)}.grade-lesson-link:hover{color:var(--kntt-blue-800);transform:translate(6px)}.grade-lesson-link:hover:before{color:var(--kntt-blue-800)}