/* ===== 全域設定：暗色主題 ===== */
:root {
  /* 主要顏色設定（可視需要微調） */
  --bg-color: #121212;
  --card-bg: #1f1f1f;
  --card-bg-alt: #242424;
  --text-color: #e5e5e5;
  --muted-text: #aaaaaa;
  --accent: #4fc3f7;
  --accent-soft: rgba(79, 195, 247, 0.16);
  --border-color: #333333;
  --danger: #ff8a80;
  --shadow-soft: 0 10px 30px rgba(0, 0, 0, 0.5);
  --radius-lg: 12px;
  --radius-md: 8px;
  --radius-pill: 999px;
}

*,
*::before,
*::after {
  box-sizing: border-box;
}

html,
body {
  margin: 0;
  padding: 0;
  background-color: var(--bg-color);
  color: var(--text-color);
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang TC",
    "Microsoft JhengHei", sans-serif;
}

/* ===== 版面 ===== */
body {
  display: flex;
  flex-direction: column;
  min-height: 100vh;
}

main {
  flex: 1;
}

.page-header,
.page-footer,
.problems-container {
  max-width: 960px;
  margin: 0 auto;
  padding: 0 16px;
}

/* ===== 頁首 ===== */
.page-header {
  padding-top: 32px;
  padding-bottom: 16px;
}

.page-header h1 {
  margin: 0 0 8px;
  font-size: 1.9rem;
  letter-spacing: 0.04em;
}

.subtitle {
  margin: 0 0 16px;
  color: var(--muted-text);
  line-height: 1.6;
}

.actions {
  display: flex;
  flex-direction: column;
  gap: 8px;
  margin-bottom: 16px;
}

.btn-primary {
  display: inline-block;
  padding: 10px 20px;
  border-radius: var(--radius-pill);
  background: linear-gradient(90deg, #4fc3f7, #80d8ff);
  color: #001018;
  text-decoration: none;
  font-weight: 600;
  text-align: center;
  box-shadow: 0 6px 20px rgba(128, 216, 255, 0.4);
  transition: transform 0.12s ease, box-shadow 0.12s ease;
}

.btn-primary:hover {
  transform: translateY(-1px);
  box-shadow: 0 10px 26px rgba(128, 216, 255, 0.5);
}

.hint {
  margin: 0;
  font-size: 0.9rem;
  color: var(--muted-text);
}

/* ===== 題目容器與卡片 ===== */
.problems-container {
  padding-bottom: 32px;
}

.problem-card {
  background: radial-gradient(circle at top left, var(--card-bg-alt), var(--card-bg));
  border-radius: var(--radius-lg);
  margin-bottom: 20px;
  padding: 16px 18px;
  border: 1px solid var(--border-color);
  box-shadow: var(--shadow-soft);
}

.problem-header {
  display: flex;
  align-items: baseline;
  gap: 8px;
  margin-bottom: 8px;
}

.problem-id {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-width: 32px;
  height: 32px;
  border-radius: var(--radius-pill);
  background-color: var(--accent-soft);
  color: var(--accent);
  font-weight: 700;
  font-size: 0.9rem;
}

.problem-title {
  font-size: 1.1rem;
  margin: 0;
}

.problem-tags {
  margin-bottom: 8px;
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
}

.tag {
  padding: 2px 8px;
  border-radius: var(--radius-pill);
  border: 1px solid var(--border-color);
  font-size: 0.75rem;
  color: var(--muted-text);
}

.tag-advanced {
  border-color: var(--danger);
  color: var(--danger);
}

.problem-description {
  margin: 4px 0 10px;
  line-height: 1.7;
  white-space: pre-line; /* 讓描述可以換行 */
}

/* ===== 測試資料區 ===== */
.samples-section {
  border-top: 1px solid var(--border-color);
  padding-top: 10px;
  margin-top: 8px;
}

.samples-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 8px;
  margin-bottom: 8px;
}

.samples-title {
  font-size: 0.95rem;
  color: var(--muted-text);
  margin: 0;
}

.toggle-btn {
  border: none;
  border-radius: var(--radius-pill);
  padding: 4px 10px;
  font-size: 0.8rem;
  background-color: rgba(255, 255, 255, 0.06);
  color: var(--muted-text);
  cursor: pointer;
  transition: background-color 0.12s ease, color 0.12s ease;
}

.toggle-btn:hover {
  background-color: rgba(255, 255, 255, 0.12);
  color: var(--text-color);
}

.samples-list {
  display: none; /* 預設收合 */
  margin: 0;
  padding: 0;
  list-style: none;
}

.samples-list.open {
  display: block; /* 展開時顯示 */
}

.sample-item {
  margin-bottom: 8px;
}

.sample-label {
  font-size: 0.85rem;
  color: var(--muted-text);
  margin-bottom: 4px;
}

.io-blocks {
  display: flex;
  flex-direction: column;
  gap: 4px;
}

/* 輸入/輸出區塊使用 <pre>，方便複製 */
.io-block {
  background-color: #101010;
  border-radius: var(--radius-md);
  border: 1px solid #2a2a2a;
  padding: 6px 8px;
  font-family: "JetBrains Mono", "Consolas", monospace;
  font-size: 0.85rem;
  white-space: pre-wrap;
  word-break: break-word;
}

.io-label {
  font-size: 0.75rem;
  color: var(--muted-text);
  margin-bottom: 2px;
}

/* ===== 頁尾 ===== */
.page-footer {
  padding: 12px 16px 20px;
  font-size: 0.85rem;
  color: var(--muted-text);
  text-align: center;
  border-top: 1px solid #1b1b1b;
}

/* ===== RWD ===== */
@media (min-width: 720px) {
  .page-header {
    padding-top: 40px;
  }

  .problem-card {
    padding: 18px 22px;
  }
}