.app-container{background:var(--bg-panel);border:1px solid #333;border-radius:16px;box-shadow:0 10px 30px rgba(0,0,0,.5);width:100%;max-width:600px;overflow:hidden;position:relative;margin-right:auto;margin-left:auto}.screen{display:none;padding:40px 30px}.screen.active{display:block;animation:fadeIn .3s ease-out}@keyframes fadeIn{from{opacity:0;transform:translateY(10px)}to{opacity:1;transform:translateY(0)}}.equation-display{font-size:4.5rem;font-weight:800;text-align:center;margin:20px 0;letter-spacing:2px;font-variant-numeric:tabular-nums}.answer-input{font-size:3rem;font-weight:700;text-align:center;background:#2a2a2a;border:2px solid #444;color:#fff;border-radius:12px;width:100%;max-width:300px;margin:0 auto;display:block;padding:10px;outline:0;transition:border-color .2s,background-color .2s}.answer-input:focus{border-color:var(--accent);background:#333;box-shadow:0 0 15px rgba(13,110,253,.3)}.answer-input::-webkit-inner-spin-button,.answer-input::-webkit-outer-spin-button{-webkit-appearance:none;margin:0}.answer-input[type=number]{appearance:textfield;-moz-appearance:textfield}.flash-correct{animation:flashGreen .4s ease-out}.flash-wrong{animation:flashRed .4s ease-out}@keyframes flashGreen{0%{background-color:rgba(25,135,84,.3)}100%{background-color:transparent}}@keyframes flashRed{0%{background-color:rgba(220,53,69,.3);transform:translateX(-5px)}25%{transform:translateX(5px)}50%{transform:translateX(-5px)}100%{background-color:transparent;transform:translateX(0)}}.game-header{display:flex;justify-content:space-between;align-items:center;margin-bottom:20px;font-size:1.2rem;font-weight:600;color:#aaa}.score-box{color:var(--accent);font-size:1.5rem}.progress{height:8px;background-color:#333;border-radius:0}.progress-bar{background-color:var(--accent);transition:width 1s linear}.stat-card{background:#252525;border:1px solid #333;border-radius:12px;padding:20px;text-align:center}.stat-val{font-size:2.5rem;font-weight:700;color:#fff}