:root{--primary-color: #2563eb;--primary-hover: #1d4ed8;--secondary-color: #64748b;--accent-color: #f59e0b;--success-color: #10b981;--danger-color: #ef4444;--background-color: #f8fafc;--surface-color: #ffffff;--text-primary: #1e293b;--text-secondary: #64748b;--text-muted: #94a3b8;--border-color: #e2e8f0;--shadow-sm: 0 1px 2px 0 rgb(0 0 0 / .05);--shadow-md: 0 4px 6px -1px rgb(0 0 0 / .1), 0 2px 4px -2px rgb(0 0 0 / .1);--shadow-lg: 0 10px 15px -3px rgb(0 0 0 / .1), 0 4px 6px -4px rgb(0 0 0 / .1);--shadow-xl: 0 20px 25px -5px rgb(0 0 0 / .1), 0 8px 10px -6px rgb(0 0 0 / .1);--border-radius: 12px;--border-radius-lg: 16px;--transition: all .3s cubic-bezier(.4, 0, .2, 1)}body.dark-theme{--background-color: #1a1a1a;--surface-color: #2d2d2d;--text-primary: #ffffff;--text-secondary: #e0e0e0;--text-muted: #b0b0b0;--border-color: #404040;--primary-color: #4dabf7;--primary-hover: #3b8fd9;--accent-color: #ffd700;--success-color: #10b981;--danger-color: #f87171;--hero-title-color: #87CEEB;--hero-subtitle-color: #b0c4de;--card-bg: #2d2d2d;--section-bg: #2d2d2d;--button-bg: #4a4a4a;--button-hover: #5a5a5a}*{box-sizing:border-box;margin:0;padding:0}body{font-family:Inter,-apple-system,BlinkMacSystemFont,Segoe UI,Roboto,sans-serif;background-color:var(--background-color);color:var(--text-primary);line-height:1.6;transition:var(--transition)}.main-content{min-height:100vh;padding-top:80px}.container{max-width:1200px;margin:0 auto;padding:0 24px}.section-header{text-align:center;margin-bottom:2rem;padding:1rem}.section-header h2{font-size:2rem;font-weight:700;color:var(--text-primary);margin-bottom:.5rem}.section-header p{color:var(--text-secondary);font-size:1.1rem;margin-bottom:1rem}.session-stats,.saved-stats{display:flex;justify-content:center;gap:2rem;flex-wrap:wrap;margin-top:1rem}.stat{display:flex;flex-direction:column;align-items:center;padding:.75rem 1.5rem;background:var(--surface-color);border:1px solid var(--border-color);border-radius:var(--border-radius);box-shadow:var(--shadow-sm);transition:var(--transition)}.stat:hover{box-shadow:var(--shadow-md);transform:translateY(-2px)}.stat-label{font-size:.875rem;color:var(--text-secondary);font-weight:500;margin-bottom:.25rem}.stat-value{font-size:1.5rem;font-weight:700;color:var(--primary-color)}.setup-section,.study-session-section{margin-bottom:3rem}.saved-section{margin-bottom:2rem}.question-selection{background:var(--surface-color);padding:2rem;border-radius:var(--border-radius);box-shadow:var(--shadow-lg);margin-bottom:2rem;max-width:600px;width:100%;margin-left:auto;margin-right:auto;border:1px solid var(--border-color)}.option-group{background:var(--surface-color);border:1px solid var(--border-color);border-radius:var(--border-radius);padding:1.5rem;margin-bottom:1rem;box-shadow:var(--shadow-sm);transition:var(--transition)}.option-group:hover{box-shadow:var(--shadow-md);border-color:var(--primary-color)}.option-group label{display:flex;align-items:center;font-weight:600;margin-bottom:.5rem;color:var(--text-primary);font-size:.95rem}.option-group .icon{margin-right:.5rem;font-size:1.1rem}.option-group select{width:100%;padding:.75rem;border:2px solid var(--border-color);border-radius:var(--border-radius);font-size:1rem;background-color:var(--surface-color);color:var(--text-primary);transition:var(--transition);cursor:pointer}.option-group select:focus{outline:none;border-color:var(--primary-color);box-shadow:0 0 0 3px #2563eb1a}.btn{display:inline-flex;align-items:center;justify-content:center;gap:.5rem;padding:.75rem 1.5rem;font-size:1rem;font-weight:600;text-align:center;text-decoration:none;border:2px solid var(--border-color);border-radius:var(--border-radius);cursor:pointer;transition:var(--transition);background-color:var(--button-bg, var(--surface-color));color:var(--text-primary);min-width:120px}.btn:hover{transform:translateY(-2px);box-shadow:var(--shadow-lg);border-color:var(--primary-color);background-color:var(--button-hover, var(--primary-color));color:#fff}.btn:active{transform:scale(.98)}.btn .icon{font-size:1.1rem}.btn-primary{background:linear-gradient(135deg,var(--primary-color) 0%,var(--primary-hover) 100%);color:#fff;border-color:var(--primary-color)}.btn-primary:hover{background:linear-gradient(135deg,var(--primary-hover) 0%,var(--primary-color) 100%);border-color:var(--primary-hover)}.btn-danger{background:linear-gradient(135deg,var(--danger-color) 0%,#dc2626 100%);color:#fff;border-color:var(--danger-color)}.btn-danger:hover{background:linear-gradient(135deg,#dc2626,#b91c1c);border-color:#dc2626}.question-selection .btn{width:100%;margin-top:1rem}.flashcard-container,#saved-flashcard-view{display:flex;flex-direction:column;justify-content:center;align-items:center;perspective:1200px;margin:2rem 0}.flip-hint-above{color:var(--text-muted);font-size:.9rem;font-style:italic;margin-bottom:1rem;opacity:.8;text-align:center}.flashcard,.saved-flashcard{width:500px;height:320px;position:relative;transform-style:preserve-3d;margin:0 auto;transition:transform .8s cubic-bezier(.4,0,.2,1);cursor:pointer;border-radius:var(--border-radius-lg);box-shadow:var(--shadow-xl)}.flashcard:hover,.saved-flashcard:hover{transform:scale(1.02)}.flashcard div,.saved-flashcard div{position:absolute;width:100%;height:100%;backface-visibility:hidden;border-radius:var(--border-radius-lg);display:flex;flex-direction:column;align-items:center;justify-content:center;padding:2rem;box-shadow:var(--shadow-lg);text-align:center;overflow-y:auto;word-wrap:break-word;white-space:normal}.flashcard-content{width:100%;height:100%;display:flex;flex-direction:column;justify-content:center;align-items:center}.flashcard-content p{font-size:1.2rem;line-height:1.6;color:var(--text-primary);max-width:100%;text-align:center;padding:0 1rem}.flashcard .front,.saved-flashcard .front{background:linear-gradient(135deg,var(--surface-color) 0%,var(--background-color) 100%);color:var(--text-primary);border:2px solid var(--border-color)}.flashcard .back,.saved-flashcard .back{background:linear-gradient(135deg,var(--primary-color) 0%,var(--primary-hover) 100%);color:#fff;transform:rotateY(180deg)}.flashcard .back .flashcard-content p,.saved-flashcard .back .flashcard-content p{color:#fffffff2}.flashcard.flipped,.saved-flashcard.flipped{transform:rotateY(180deg)}.flashcard-controls,.navigation-buttons{display:flex;justify-content:center;gap:1rem;margin:2rem 0;flex-wrap:wrap}.flashcard-controls .btn,.navigation-buttons .btn{flex:1;min-width:140px;max-width:200px}#back-to-study{display:block;margin:2rem auto 0;max-width:200px}#theme-toggle{position:fixed;top:20px;left:20px;z-index:1000;background:var(--surface-color);border:2px solid var(--border-color);color:var(--accent-color);font-size:1.5rem;cursor:pointer;padding:8px;border-radius:50%;transition:var(--transition);box-shadow:var(--shadow-md)}#theme-toggle:hover{background-color:var(--primary-color);color:#fff;transform:scale(1.1)}body.dark-theme .hero-section{background:linear-gradient(135deg,var(--card-bg) 0%,var(--section-bg) 100%);border-bottom:1px solid var(--border-color)}body.dark-theme .question-selection{background:linear-gradient(135deg,var(--surface-color) 0%,var(--card-bg) 100%);border:1px solid var(--border-color);box-shadow:0 10px 30px #0000004d}body.dark-theme .option-group{background:var(--surface-color);border:1px solid var(--border-color)}body.dark-theme .option-group:hover{border-color:var(--primary-color);box-shadow:0 8px 25px #0006}body.dark-theme .stat{background:var(--surface-color);border:1px solid var(--border-color)}body.dark-theme .flashcard .front,body.dark-theme .saved-flashcard .front{background:linear-gradient(135deg,var(--surface-color) 0%,var(--card-bg) 100%);border:2px solid var(--border-color)}body.dark-theme .flashcard .back,body.dark-theme .saved-flashcard .back{background:linear-gradient(135deg,var(--primary-color) 0%,var(--primary-hover) 100%)}@media (max-width: 768px){.flashcard,.saved-flashcard{width:90%;height:280px}.flashcard-controls,.navigation-buttons{flex-direction:column;align-items:center}.flashcard-controls .btn,.navigation-buttons .btn{width:100%;max-width:300px}.session-stats,.saved-stats{flex-direction:column;align-items:center;gap:1rem}.stat{width:100%;max-width:200px}#theme-toggle{top:15px;left:15px;font-size:1.2rem;padding:6px}}@media (max-width: 480px){.question-selection{padding:1.5rem}.flashcard,.saved-flashcard{height:250px}.flashcard-content h3{font-size:1.3rem}.flashcard-content p{font-size:1rem}.section-header h2{font-size:1.5rem}}::-webkit-scrollbar{width:8px}::-webkit-scrollbar-track{background:var(--background-color);border-radius:4px}::-webkit-scrollbar-thumb{background:var(--border-color);border-radius:4px}::-webkit-scrollbar-thumb:hover{background:var(--text-muted)}@keyframes fadeInUp{0%{opacity:0;transform:translateY(30px)}to{opacity:1;transform:translateY(0)}}.flashcard,.saved-flashcard{animation:fadeInUp .6s ease-out}.flashcard.loading,.saved-flashcard.loading{opacity:.7;pointer-events:none}.flashcard.loading:after,.saved-flashcard.loading:after{content:"";position:absolute;top:50%;left:50%;width:30px;height:30px;margin:-15px 0 0 -15px;border:3px solid var(--border-color);border-top:3px solid var(--primary-color);border-radius:50%;animation:spin 1s linear infinite}@keyframes spin{0%{transform:rotate(0)}to{transform:rotate(360deg)}}