:root{font-family:system-ui,-apple-system,BlinkMacSystemFont,Segoe UI,Roboto,Oxygen,Ubuntu,Cantarell,sans-serif;line-height:1.5;font-weight:400;font-synthesis:none;text-rendering:optimizeLegibility;-webkit-font-smoothing:antialiased;-moz-osx-font-smoothing:grayscale}*{margin:0;padding:0;box-sizing:border-box}body{margin:0;min-width:320px;min-height:100vh;background:linear-gradient(135deg,#f5f7fa,#c3cfe2);color:#333}#root{width:100%}button{font-family:inherit;cursor:pointer}button:focus,button:focus-visible{outline:2px solid #667eea;outline-offset:2px}*{box-sizing:border-box}.app{max-width:900px;margin:0 auto;padding:2rem;text-align:center;min-height:100vh;display:flex;flex-direction:column;align-items:center}h1{font-size:2.5rem;margin-bottom:3rem;color:#333}.flashcard-container{margin-bottom:3rem;display:flex;flex-direction:column;align-items:center;gap:2rem}.flashcard{width:400px;height:300px;perspective:1000px;cursor:pointer}.flashcard-inner{position:relative;width:100%;height:100%;transition:transform .15s ease-out;transform-style:preserve-3d;-webkit-user-select:none;user-select:none}.flashcard-inner.flipped{transform:rotateY(180deg)}.flashcard-front,.flashcard-back{position:absolute;width:100%;height:100%;backface-visibility:hidden;border-radius:16px;display:flex;flex-direction:column;justify-content:center;align-items:center;padding:3rem;box-shadow:0 2px 4px #667eea0a,0 4px 8px #667eea0f;border:2px solid #e0e0e0}.flashcard-front{background:#fff;color:#000}.flashcard-back{background:#fff;color:#000;transform:rotateY(180deg)}.problem,.answer{font-size:4rem;font-weight:700;margin-bottom:1rem}.hint{font-size:.9rem;opacity:.8;margin-top:2rem}.no-numbers{width:400px;height:300px;display:flex;align-items:center;justify-content:center;background:#fff;color:#000;font-size:1.5rem;border-radius:16px;padding:3rem;box-shadow:0 2px 4px #667eea0a,0 4px 8px #667eea0f;border:2px solid #e0e0e0}.navigation-buttons{display:flex;gap:1rem;align-items:center}.next-button,.prev-button{padding:.75rem 2rem;font-size:1.1rem;font-weight:600;color:#fff;background:linear-gradient(135deg,#667eea,#764ba2);border:none;border-radius:8px;cursor:pointer;transition:transform .2s,box-shadow .2s;box-shadow:0 2px 4px #667eea26}.next-button:hover,.prev-button:hover{transform:translateY(-2px);box-shadow:0 4px 8px #667eea33}.next-button:active,.prev-button:active{transform:translateY(0);box-shadow:0 1px 2px #667eea26}.prev-button:disabled{background:linear-gradient(135deg,silver,#a0a0a0);cursor:not-allowed;opacity:.5}.prev-button:disabled:hover{transform:none;box-shadow:0 2px 4px #667eea14}.number-toggles{width:100%;max-width:600px;padding:2rem;background:#fff;border-radius:16px;box-shadow:0 2px 4px #667eea0a,0 4px 8px #667eea0f;border:2px solid #e0e0e0}.number-toggles-header{display:flex;justify-content:space-between;align-items:center;margin-bottom:1.5rem}.number-toggles h3{margin:0;color:#333;font-size:1.5rem}.select-all-button{padding:.5rem 1rem;font-size:.9rem;font-weight:600;color:#fff;background:linear-gradient(135deg,#667eea,#764ba2);border:none;border-radius:8px;cursor:pointer;transition:transform .2s,box-shadow .2s;box-shadow:0 2px 4px #667eea26}.select-all-button:hover{transform:translateY(-1px);box-shadow:0 4px 8px #667eea33}.select-all-button:active{transform:translateY(0);box-shadow:0 1px 2px #667eea26}.header-controls{display:flex;gap:1rem;align-items:center}.only-mode-toggle{display:flex;align-items:center;gap:.5rem;cursor:pointer;-webkit-user-select:none;user-select:none}.only-mode-toggle input[type=checkbox]{width:18px;height:18px;cursor:pointer;accent-color:#667eea}.toggle-label{font-size:.9rem;font-weight:600;color:#333}.toggle-grid{display:grid;grid-template-columns:repeat(6,1fr);gap:.75rem}.toggle-button{width:100%;aspect-ratio:1;font-size:1.25rem;font-weight:600;border:2px solid #ddd;border-radius:8px;background:#fff;color:#999;cursor:pointer;transition:all .2s}.toggle-button:hover{border-color:#667eea;transform:translateY(-2px);box-shadow:0 2px 4px #667eea1f}.toggle-button.active{background:linear-gradient(135deg,#667eea,#764ba2);color:#fff;border-color:#667eea;box-shadow:0 2px 4px #667eea26}.toggle-button.active:hover{box-shadow:0 4px 8px #667eea33}@media(max-width:600px){.flashcard{width:300px;height:225px}.flashcard-front,.flashcard-back{padding:2rem}.no-numbers{width:300px;height:225px;font-size:1.2rem;padding:2rem}.problem,.answer{font-size:3rem}.toggle-grid{grid-template-columns:repeat(4,1fr)}h1{font-size:2rem}}