:root{
  --bg:#f7f7fb;
  --card:#ffffff;
  --accent:#2b6cb0;
  --muted:#6b7280;
}
*{box-sizing:border-box}
html,body{height:100%}
.app-wrap{width:100%;max-width:420px}
body{
  margin:0; font-family:Inter, system-ui, -apple-system, "Segoe UI", Roboto, "Helvetica Neue", Arial;
  background:var(--bg); color:#111; display:flex; align-items:center; justify-content:center; padding:16px;
}
.screen{width:100%;background:var(--card);border-radius:16px;box-shadow:0 6px 22px rgba(16,24,40,0.08);position:relative;overflow:auto;-webkit-overflow-scrolling:touch}
.screen.hidden{display:none}
.hidden{display:none}
.app-title{margin:20px;text-align:center;font-size:20px}
.panel{padding:12px 18px;border-top:1px solid #f0f0f3}
.ops{display:flex;gap:8px;flex-wrap:wrap}
.op-btn{flex:1 1 48%;padding:12px;border-radius:10px;border:1px solid #e6e9ef;background:white;font-size:16px}
.op-btn.active{background:var(--accent);color:white;border-color:var(--accent)}
.op-btn.disabled{opacity:0.45}
.modes{display:flex;gap:12px;padding-top:8px}
.mode-btn{flex:1;padding:12px;border-radius:10px;border:1px solid #e6e9ef;background:white;font-size:16px}
.mode-btn.active{background:#111;color:white}
.hint{padding:12px 18px;color:var(--muted);font-size:14px}

.settings{display:flex;flex-direction:column;gap:8px}
.settings label{display:flex;justify-content:space-between;align-items:center;gap:12px}
.settings input{width:120px;padding:8px;border-radius:8px;border:1px solid #e6e9ef}
.settings-actions{display:flex;gap:8px;margin-top:6px}
.settings.collapsed{display:none}
.collapsed{display:none}
.small{font-size:13px;padding:6px 8px;border-radius:8px;border:1px solid #e6e9ef;background:white}

.progress-outer{height:12px;background:#eef3fb;border-radius:8px;overflow:hidden;margin:8px 14px}
.progress-inner{height:100%;background:var(--accent);width:0%}


.play-header{display:flex;align-items:center;justify-content:space-between;padding:10px 14px;border-bottom:1px solid #f0f0f3}
.play-header .small{background:transparent;border:0;color:var(--accent);font-weight:600}
.problem-area{padding:18px;text-align:center}
.problem{font-size:44px;font-weight:700;margin:6px 0}
.problem.big{font-size:64px}
.timer{font-size:18px;color:var(--muted);margin-bottom:8px}
.answer-area{padding:8px 14px 20px}
.answer{min-height:56px;font-size:30px;text-align:center;padding:8px;border-radius:8px;background:#f6f7fb;margin-bottom:10px}
.feedback{height:22px;color:var(--muted)}
.keypad{display:grid;gap:10px}
.row{display:flex;gap:8px}
.key{flex:1;padding:16px;border-radius:12px;border:1px solid #e6e9ef;background:white;font-size:22px}
.key.large{padding:18px;font-size:24px}
.key.special{background:#fff7ed}
.submit-btn{flex:1;padding:16px;border-radius:12px;background:var(--accent);color:white;font-weight:700;font-size:18px;border:0}
.score{font-weight:700}

.history-list{display:flex;flex-direction:column;gap:8px}
.history-item{padding:10px;border-radius:8px;background:#f6f7fb;border:1px solid #e9eef6}
.history-meta{font-size:12px;color:var(--muted)}

.summary{padding:18px;text-align:center}
.summary h2{margin:6px 0}
.summary p{font-size:18px}

@media (orientation:portrait){
  .screen{max-height:94vh}
}

/* Mobile-specific: ensure the app fills viewport and screens scroll vertically */
@media (max-width:480px){
  body{padding:0}
  .app-wrap{max-width:100%;height:100vh}
  .screen{height:100vh;max-height:none;border-radius:0;overflow:auto;-webkit-overflow-scrolling:touch}
}