:root {
  --bg:#f6f8fb;
  --card:#fff;
  --accent:#5b8def;
  --accent-2:#7bd389;
  --muted:#6b7280;
  --border:#e6e9ef;
  --text:#111;
  --shadow:0 6px 18px rgba(12,20,40,0.06);
  --radius:12px;
  --radius-sm:8px;
  --radius-lg:16px;
  --font:Inter, system-ui, -apple-system, 'Segoe UI', Roboto, Arial;
}

*{box-sizing:border-box}

body{
  font-family:var(--font);
  background:var(--bg);
  margin:0;
  padding:24px;
  color:var(--text);
}

.app{
  max-width:980px;
  margin:0 auto;
}

header{
  display:flex;
  gap:16px;
  align-items:center;
  margin-bottom:16px;
  flex-wrap:wrap;
}
h1{
  font-size:20px;
  margin:0;
}
.sub{
  color:var(--muted);
  font-size:13px;
}

.controls{
  display:flex;
  gap:8px;
  margin-bottom:12px;
  flex-wrap:wrap;
}
.row{
  display:flex;
  gap:12px;
  align-items:flex-start;
  flex-wrap:wrap;
}

.card{
  background:var(--card);
  padding:16px;
  border-radius:var(--radius);
  box-shadow:var(--shadow);
}

button{
  background:var(--accent);
  color:#fff;
  border:0;
  padding:8px 12px;
  border-radius:var(--radius-sm);
  cursor:pointer;
  font-size:14px;
  line-height:1.2;
}
button.secondary{
  background:#eef3ff;
  color:var(--accent);
  border:1px solid rgba(91,141,239,0.12);
}
button:disabled{
  opacity:.5;
  cursor:not-allowed;
}
.block-btn{
  display:block;
  min-width:72px;
  text-align:center;
}

.mode-btn{
  padding:6px 10px;
  border-radius:var(--radius-sm);
  border:1px solid var(--border);
  background:#fff;
  font-size:14px;
}
label{
  font-size:13px;
  font-weight:500;
  color:var(--text);
}

.big-problem{
  font-size:44px;
  margin:8px 0;
  line-height:1.15;
  font-weight:600;
  word-break:break-word;
}

.answer-row{
  display:flex;
  gap:8px;
  align-items:center;
  margin-top:10px;
  flex-wrap:wrap;
}
input[type=number],
input[type=text]{
  width:140px;
  padding:10px;
  border-radius:10px;
  border:1px solid var(--border);
  font-size:16px;
  line-height:1.2;
}

.timer{
  margin-left:auto;
  color:var(--muted);
  font-size:13px;
  min-width:70px;
  text-align:right;
}

.tenframe{
  display:grid;
  grid-template-columns:repeat(5,36px);
  gap:6px;
  margin-top:8px;
}
.cell{
  width:36px;
  height:36px;
  border-radius:6px;
  background:#f1f5f9;
  display:flex;
  align-items:center;
  justify-content:center;
  font-weight:600;
  font-size:14px;
}
.cell.filled{
  background:var(--accent);
  color:#fff;
}
.cell.crossed{
  background:#fff;
  color:#d1d5db;
  text-decoration:line-through;
}

.feedback{
  margin-top:8px;
  font-weight:700;
  font-size:15px;
}
.hint{
  margin-top:6px;
  color:var(--muted);
  font-size:14px;
}

.stats{
  display:flex;
  gap:8px;
  flex-wrap:wrap;
}
.stat{
  background:#fff;
  padding:10px;
  border-radius:var(--radius-sm);
  min-width:120px;
  border:1px solid var(--border);
  font-size:13px;
  line-height:1.3;
}
.stat.sm{
  min-width:auto;
  padding:6px 10px;
}

.kbd{
  font-family:ui-monospace,SFMono-Regular,Menlo,monospace;
  background:#f3f4f6;
  border:1px solid #e5e7eb;
  border-bottom-width:3px;
  border-radius:6px;
  padding:2px 6px;
  font-size:12px;
  line-height:1.2;
}

.instructions{
  margin-top:10px;
  color:var(--muted);
  font-size:13px;
  line-height:1.4;
}

/* History table */
.history-wrap{
  margin-top:12px;
  max-height:220px;
  overflow:auto;
  border:1px solid var(--border);
  border-radius:var(--radius-sm);
}
.history-table{
  width:100%;
  border-collapse:collapse;
  font-size:13px;
}
.history-table th{
  position:sticky;
  top:0;
  background:#fff;
  text-align:left;
  font-weight:600;
  border-bottom:1px solid var(--border);
  padding:6px 8px;
  font-size:12px;
  white-space:nowrap;
}
.history-table td{
  border-bottom:1px solid var(--border);
  padding:6px 8px;
  vertical-align:top;
  line-height:1.4;
  word-break:break-word;
}
.history-table tr.correct td{
  background:rgba(123,211,137,0.08);
}
.history-table tr.wrong td{
  background:rgba(255,0,0,0.03);
  color:#7a0000;
  font-weight:500;
}

/* overlay for session choice */
.overlay{
  position:fixed;
  inset:0;
  background:rgba(0,0,0,0.4);
  display:flex;
  align-items:center;
  justify-content:center;
  z-index:9999;
  padding:16px;
}
.overlay-card{
  background:#fff;
  border-radius:var(--radius-lg);
  box-shadow:var(--shadow);
  padding:24px;
  max-width:320px;
  width:100%;
  text-align:center;
  font-family:var(--font);
}
.overlay-card h2{
  margin:0 0 8px;
  font-size:20px;
}
.overlay-card p{
  margin:0 0 16px;
  font-size:14px;
  color:var(--muted);
  line-height:1.4;
}
.overlay-actions{
  display:flex;
  flex-direction:column;
  gap:8px;
}
.overlay-actions button{
  width:100%;
  font-size:14px;
}

/* "hint-slot" so Hint button lines up with other labeled controls */
.hint-slot{
  display:flex;
  flex-direction:column;
  justify-content:flex-end;
  align-items:flex-start;
  min-width:72px;
  margin-top:18px; /* visually lines up with bottom of labeled fields */
}

@media (max-width:640px){
  .row{
    flex-direction:column;
    align-items:flex-start;
  }
  .big-problem{
    font-size:36px;
  }
  .timer{
    margin-left:0;
    text-align:left;
  }
}