:root {
  --bg: #f3f6fb;
  --card: #ffffff;
  --text: #172033;
  --muted: #5b667a;
  --border: #d8e0ee;
  --primary: #2563eb;
  --primary-dark: #1d4ed8;
  --secondary: #eef2ff;
  --secondary-text: #1e3a8a;
  --good: #15803d;
  --medium: #c2410c;
  --bad: #dc2626;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-height: 100vh;
  background: radial-gradient(circle at top, #e0ecff 0%, var(--bg) 45%, #eef2f7 100%);
  color: var(--text);
  font-family: Arial, Helvetica, sans-serif;
}

.app {
  width: 100%;
  min-height: 100vh;
  display: flex;
  justify-content: center;
  align-items: flex-start;
  padding: 28px 16px;
}

.card {
  width: min(900px, 100%);
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: 24px;
  box-shadow: 0 18px 45px rgba(20, 30, 55, 0.12);
  padding: 24px;
}

h1 {
  margin: 0;
  text-align: center;
  font-size: clamp(28px, 4vw, 42px);
  letter-spacing: -0.03em;
}

.subtitle {
  margin: 10px auto 20px;
  text-align: center;
  color: var(--muted);
  font-size: 17px;
}

.info-row {
  display: grid;
  grid-template-columns: 1fr 1.4fr;
  gap: 12px;
  margin-bottom: 16px;
}

.target-box,
.hint-box {
  border: 1px solid var(--border);
  border-radius: 16px;
  padding: 14px 16px;
  background: #f8fbff;
  font-size: 16px;
}

.target-box {
  font-weight: 700;
  color: #0f172a;
}

.canvas-wrap {
  width: 100%;
  overflow: hidden;
  border: 1px solid var(--border);
  border-radius: 18px;
  background: white;
}

canvas {
  width: 100%;
  height: auto;
  display: block;
  touch-action: none;
  cursor: crosshair;
}

.buttons {
  display: flex;
  justify-content: center;
  gap: 12px;
  flex-wrap: wrap;
  margin: 18px 0;
}

button {
  appearance: none;
  border: none;
  border-radius: 14px;
  background: var(--primary);
  color: white;
  padding: 12px 18px;
  min-width: 150px;
  font-size: 16px;
  font-weight: 700;
  cursor: pointer;
  transition: transform 0.15s ease, background 0.15s ease, box-shadow 0.15s ease;
  box-shadow: 0 10px 18px rgba(37, 99, 235, 0.2);
}

button:hover {
  background: var(--primary-dark);
  transform: translateY(-1px);
}

button:active {
  transform: translateY(0);
}

button.secondary {
  background: var(--secondary);
  color: var(--secondary-text);
  box-shadow: none;
}

.result {
  min-height: 72px;
  display: flex;
  align-items: center;
  justify-content: center;
  text-align: center;
  white-space: pre-line;
  border-radius: 18px;
  background: #f8fafc;
  border: 1px solid var(--border);
  padding: 18px;
  font-size: clamp(22px, 3vw, 32px);
  font-weight: 800;
  color: #111827;
}

.result.good {
  color: var(--good);
}

.result.medium {
  color: var(--medium);
}

.result.bad {
  color: var(--bad);
}

.math-note {
  margin: 14px 0 0;
  text-align: center;
  color: var(--muted);
  font-size: 14px;
}

@media (max-width: 720px) {
  .card {
    padding: 16px;
    border-radius: 18px;
  }

  .info-row {
    grid-template-columns: 1fr;
  }

  button {
    width: 100%;
  }
}