.mode-btn { border-width: 2px; font-weight: 800; opacity: 0.6; transition: all 0.2s; }
    .mode-btn.active { opacity: 1; transform: scale(1.05); }
    #play-a.active { border-color: #00ffcc; color: #00ffcc; box-shadow: 0 0 20px rgba(0, 255, 204, 0.2); }
    #play-b.active { border-color: #ffcc00; color: #ffcc00; box-shadow: 0 0 20px rgba(255, 204, 0, 0.2); }
    .bg-black { background-color: #000; }