.difficulty-selector-container{background:linear-gradient(135deg,#4ecdc4 0%,#44a08d 100%);flex-direction:column;justify-content:center;align-items:center;min-height:100vh;padding:20px;display:flex}.back-button-difficulty{cursor:pointer;color:#44a08d;z-index:10;background:#fff;border:none;border-radius:10px;padding:12px 25px;font-size:1rem;font-weight:700;transition:all .3s;position:absolute;top:90px;left:20px;box-shadow:0 4px 10px #0003}.back-button-difficulty:hover{transform:translateY(-2px);box-shadow:0 6px 15px #0000004d}.difficulty-selector-content{text-align:center;width:100%;max-width:900px}.difficulty-selector-content h1{color:#fff;text-shadow:2px 2px 8px #0003;margin-bottom:15px;font-size:2.8rem;animation:.6s slideDown}.difficulty-selector-content p{color:#fffffff2;margin-bottom:50px;font-size:1.2rem;animation:.8s slideDown}.difficulty-cards{grid-template-columns:repeat(auto-fit,minmax(300px,1fr));gap:30px;display:grid}.difficulty-card{cursor:pointer;text-align:center;background:#fff;border-radius:20px;padding:40px 30px;transition:all .4s cubic-bezier(.68,-.55,.265,1.55);position:relative;box-shadow:0 10px 30px #00000026}.difficulty-grade-badge{color:#666;background:#f0f0f0;border-radius:50px;padding:5px 12px;font-size:.75rem;font-weight:700;position:absolute;top:14px;right:14px}.difficulty-grade-badge.new{color:#fff;background:linear-gradient(135deg,#667eea 0%,#764ba2 100%)}.difficulty-card:hover,.difficulty-card.hovered{transform:translateY(-15px)scale(1.05);box-shadow:0 20px 50px #00000040}.difficulty-icon{margin-bottom:20px;font-size:4rem;animation:2s ease-in-out infinite bounce;display:block}.difficulty-card:hover .difficulty-icon,.difficulty-card.hovered .difficulty-icon{animation:.6s ease-in-out spin}.difficulty-card h2{color:#333;margin-bottom:10px;font-size:1.8rem;font-weight:700}.difficulty-card p{color:#666;margin-top:0;margin-bottom:20px;font-size:1rem}.example{color:#333;background:#f0f0f0;border-radius:10px;margin-bottom:20px;padding:12px 15px;font-size:1.1rem;font-weight:600}.start-button{color:#fff;cursor:pointer;background:linear-gradient(135deg,#4ecdc4 0%,#44a08d 100%);border:none;border-radius:50px;padding:12px 30px;font-size:1rem;font-weight:700;transition:all .3s;box-shadow:0 6px 20px #f5576c66}.start-button:hover{transform:translateY(-2px);box-shadow:0 8px 25px #f5576c99}@keyframes slideDown{0%{opacity:0;transform:translateY(-30px)}to{opacity:1;transform:translateY(0)}}@keyframes bounce{0%,to{transform:translateY(0)}50%{transform:translateY(-10px)}}@keyframes spin{0%{transform:rotate(0)scale(1)}to{transform:rotate(360deg)scale(1.1)}}@media (max-width:768px){.difficulty-selector-content h1{font-size:2rem}.difficulty-cards{grid-template-columns:1fr;gap:20px}.difficulty-card{padding:30px 20px}}