:root{--bg-color:#f0f4f8;--text-primary:#1e293b;--text-secondary:#64748b;--primary-color:#3b82f6;--primary-hover:#2563eb;--grade-again:#ef4444;--grade-hard:#f59e0b;--grade-good:#10b981;--grade-easy:#3b82f6;--shadow-sm:0 1px 2px 0 #0000000d;--shadow-md:0 4px 6px -1px #0000001a, 0 2px 4px -2px #0000001a;--shadow-lg:0 10px 15px -3px #0000001a, 0 4px 6px -4px #0000001a;--shadow-inner:inset 0 2px 4px 0 #0000000d;--radius-sm:.375rem;--radius-md:.5rem;--radius-lg:.75rem;--radius-xl:1rem;--radius-full:9999px;--transition-fast:.15s cubic-bezier(.4, 0, .2, 1);--transition-normal:.3s cubic-bezier(.4, 0, .2, 1)}*{box-sizing:border-box;-webkit-tap-highlight-color:transparent}body{background:var(--bg-color);color:var(--text-primary);-webkit-font-smoothing:antialiased;margin:0;font-family:Inter,Noto Sans JP,sans-serif;line-height:1.5}h1,h2,h3,p{margin-top:0}.screen{flex-direction:column;max-width:480px;min-height:100vh;margin:0 auto;padding:2rem 1.25rem;display:flex}button{font:inherit;cursor:pointer;transition:transform var(--transition-fast), background-color var(--transition-fast), box-shadow var(--transition-fast);outline:none}button:active{transform:scale(.96)}@keyframes fadeIn{0%{opacity:0;transform:translateY(10px)}to{opacity:1;transform:translateY(0)}}@keyframes pop{0%{opacity:0;transform:scale(.5)}60%{opacity:1;transform:scale(1.1)}to{opacity:1;transform:scale(1)}}.animate-fade-in{animation:.4s cubic-bezier(.16,1,.3,1) forwards fadeIn}.progress-bar{border-radius:var(--radius-full);height:.75rem;box-shadow:var(--shadow-inner);background:#e2e8f0;margin-bottom:2rem;position:relative;overflow:hidden}.progress-bar__fill{border-radius:var(--radius-full);background:linear-gradient(90deg,#60a5fa,#3b82f6);height:100%;transition:width .4s cubic-bezier(.34,1.56,.64,1)}.progress-bar__label{display:none}.breadcrumb{color:var(--text-secondary);text-align:center;margin-bottom:1rem;font-size:.875rem;font-weight:500}.flashcard-container{flex-direction:column;flex:1;display:flex}.flashcard{border-radius:var(--radius-xl);box-shadow:var(--shadow-lg);text-align:center;z-index:10;background:#fff;margin-bottom:2rem;padding:2rem 1.5rem;position:relative}.question-text{color:var(--text-primary);margin-bottom:0;font-size:1.35rem;font-weight:500;line-height:1.8}.blank{text-align:center;border-bottom:3px solid var(--primary-color);min-width:4em;color:var(--primary-color);transition:color var(--transition-normal);margin:0 .25rem;padding-bottom:.2rem;font-weight:700;display:inline-block}.reveal-button{background:var(--primary-color);color:#fff;border-radius:var(--radius-lg);width:100%;box-shadow:var(--shadow-md);border:none;padding:1.25rem;font-size:1.1rem;font-weight:600}.reveal-button:hover{background:var(--primary-hover)}.grade-buttons-container{animation:.3s ease-out forwards fadeIn}.grade-buttons{grid-template-columns:repeat(2,1fr);gap:.75rem;display:grid}.grade-btn{border-radius:var(--radius-lg);color:#fff;box-shadow:var(--shadow-md);border:none;flex-direction:column;justify-content:center;align-items:center;gap:.5rem;padding:1rem .5rem;font-size:1rem;font-weight:600;display:flex}.grade-btn-again{background:var(--grade-again)}.grade-btn-hard{background:var(--grade-hard)}.grade-btn-good{background:var(--grade-good)}.grade-btn-easy{background:var(--grade-easy)}.grade-btn .emoji{font-size:1.5rem}.home-screen{gap:1.5rem;padding-top:2.5rem}.home-screen h1{text-align:center;color:var(--text-primary);margin-bottom:1rem;font-size:1.8rem;font-weight:700}.primary-cta{background:var(--primary-color);color:#fff;border-radius:var(--radius-xl);border:none;padding:1.25rem;font-size:1.15rem;font-weight:700;box-shadow:0 10px 20px -5px #3b82f666}.primary-cta:hover{background:var(--primary-hover);box-shadow:0 10px 25px -5px #3b82f680}.secondary-nav{flex-direction:column;gap:.75rem;display:flex}.secondary-nav button{border-radius:var(--radius-lg);color:var(--text-primary);box-shadow:var(--shadow-sm);background:#fff;border:1px solid #e2e8f0;justify-content:center;align-items:center;gap:.5rem;padding:1.1rem;font-weight:600;display:flex}.secondary-nav button:hover{background:#f8fafc}.chapter-count{text-align:center;color:var(--text-secondary);margin-top:auto;padding-top:2rem;font-size:.9rem}.today-done-message{text-align:center;color:#065f46;border-radius:var(--radius-md);background:#ecfdf5;padding:1rem;font-size:.95rem;font-weight:600}.completion-screen{flex-direction:column;flex:1;justify-content:center;align-items:center;display:flex}.completion-screen__emoji{margin-bottom:1.5rem;font-size:5rem;animation:.6s cubic-bezier(.34,1.56,.64,1) pop}.completion-screen h2{color:var(--text-primary);margin-bottom:2rem;font-size:1.5rem}.completion-screen button{background:var(--text-primary);color:#fff;border-radius:var(--radius-lg);border:none;width:100%;padding:1.25rem;font-size:1.1rem;font-weight:600}.chapter-list{flex-direction:column;gap:.75rem;padding:0;list-style:none;display:flex}.chapter-list button{border-radius:var(--radius-lg);width:100%;box-shadow:var(--shadow-sm);color:var(--text-primary);text-align:left;background:#fff;border:none;padding:1.1rem;font-weight:500}.chapter-list button:disabled{color:#94a3b8;box-shadow:none;background:#f1f5f9}.chapter-load-warning{color:#ef4444;border-radius:var(--radius-md);text-align:center;background:#fef2f2;padding:.75rem;font-size:.85rem}.session-error{color:#ef4444;text-align:center;border-radius:var(--radius-lg);background:#fef2f2;margin-top:3rem;padding:1.5rem;font-weight:600}