:root {
  --bg: #0d1117;
  --panel: #161b22;
  --border: #30363d;
  --text: #e6edf3;
  --muted: #8b949e;
  --accent: #4ade80;
  --danger: #f87171;
}

* { box-sizing: border-box; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: "Noto Sans JP", system-ui, sans-serif;
  line-height: 1.7;
}

.app-header {
  padding: 24px 20px 12px;
  border-bottom: 1px solid var(--border);
}

.app-header h1 {
  margin: 0 0 4px;
  font-size: 1.3rem;
}

.tagline {
  margin: 0;
  color: var(--muted);
  font-size: 0.85rem;
}

.app-main {
  max-width: 640px;
  margin: 0 auto;
  padding: 20px 16px 60px;
}

.card {
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 16px;
  margin-bottom: 16px;
}

.source-note {
  font-size: 0.75rem;
  color: var(--muted);
  border-left: 3px solid var(--border);
  padding-left: 8px;
  margin-top: 8px;
}

.ai-note {
  border: 1px dashed var(--accent);
  border-radius: 10px;
  padding: 12px;
  margin-top: 12px;
  background: rgba(74, 222, 128, 0.08);
}

.ai-note::before {
  content: "AI解説（公式解説ではありません）";
  display: block;
  font-size: 0.75rem;
  color: var(--accent);
  margin-bottom: 6px;
}

button {
  background: var(--accent);
  color: #0d1117;
  border: none;
  border-radius: 8px;
  padding: 10px 16px;
  font-weight: 700;
  cursor: pointer;
  margin: 4px 4px 4px 0;
}

button.secondary {
  background: transparent;
  color: var(--text);
  border: 1px solid var(--border);
}

.mistake-options button {
  display: block;
  width: 100%;
  text-align: left;
  background: var(--panel);
  color: var(--text);
  border: 1px solid var(--border);
  margin-bottom: 8px;
}

.app-footer {
  text-align: center;
  color: var(--muted);
  font-size: 0.75rem;
  padding: 20px;
}

.calc-toggle {
  position: fixed;
  right: 16px;
  bottom: 16px;
  width: 56px;
  height: 56px;
  border-radius: 50%;
  font-size: 1.4rem;
  padding: 0;
  margin: 0;
  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.4);
  z-index: 20;
}

.calc-panel {
  position: fixed;
  right: 16px;
  bottom: 84px;
  width: min(300px, calc(100vw - 32px));
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 12px;
  box-shadow: 0 8px 24px rgba(0, 0, 0, 0.5);
  z-index: 20;
}

.calc-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  font-size: 0.85rem;
  color: var(--muted);
  margin-bottom: 8px;
}

.calc-close {
  background: transparent;
  color: var(--muted);
  border: none;
  padding: 2px 6px;
  margin: 0;
  font-size: 1rem;
}

.calc-display {
  width: 100%;
  box-sizing: border-box;
  background: var(--bg);
  color: var(--text);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 10px;
  font-size: 1.2rem;
  text-align: right;
  margin-bottom: 8px;
}

.calc-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 6px;
}

.calc-grid button {
  margin: 0;
  padding: 12px 0;
  background: var(--bg);
  color: var(--text);
  border: 1px solid var(--border);
  font-weight: 500;
}

.calc-insert {
  display: block;
  width: 100%;
  margin: 8px 0 0;
}

.intro-card p {
  margin: 0 0 12px;
}

.intro-steps {
  margin: 0 0 20px;
  padding-left: 20px;
}

.intro-steps li {
  margin-bottom: 6px;
}

.intro-card #start-btn {
  width: 100%;
  font-size: 1rem;
  padding: 14px 16px;
}