/* Bobo Labs — Formula article layer. Extends article.css with formula-specific blocks. */

/* Tier badge（Free / Pro 標籤）---------------------------------------------- */
.formula-tier {
  display: inline-block;
  font-family: var(--font-mono);
  font-size: 0.75rem;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  padding: 0.18rem 0.55rem;
  border-radius: 999px;
  margin-left: 0.5rem;
  vertical-align: 0.18em;
}
.formula-tier--free {
  background: oklch(95% 0.04 150);
  color: oklch(35% 0.14 150);
}
.formula-tier--pro {
  background: oklch(94% 0.06 70);
  color: oklch(40% 0.18 70);
}

/* 公式展示 box（LaTeX-style 大號顯示）-------------------------------------- */
.formula-box {
  margin: 2rem 0 1.25rem;
  padding: 1.75rem 1.5rem;
  background: oklch(99% 0 0);
  border: 1px solid var(--color-line);
  border-left: 3px solid var(--color-accent);
  border-radius: 0.5rem;
  text-align: center;
}
.formula-box-eq {
  font-family: "Times New Roman", "Cambria Math", "STIX Two Math", serif;
  font-size: clamp(1.5rem, 1rem + 1.5vw, 2.25rem);
  font-style: italic;
  letter-spacing: 0.02em;
  color: var(--color-ink);
  line-height: 1.3;
}
.formula-box-note {
  font-family: var(--font-mono);
  font-size: 0.875rem;
  color: var(--color-muted);
  margin-top: 0.6rem;
  font-style: normal;
}
.formula-box-eq sup, .formula-box-eq sub { font-size: 0.6em; line-height: 0; }
.formula-box-eq em { font-style: italic; }

/* 變數說明表 ------------------------------------------------------------- */
.formula-vars {
  margin: 1rem 0 2rem;
  border-collapse: collapse;
  width: 100%;
  font-size: 0.95rem;
}
.formula-vars th, .formula-vars td {
  padding: 0.6rem 0.8rem;
  border-bottom: 1px solid var(--color-line);
  text-align: left;
}
.formula-vars th {
  font-family: var(--font-mono);
  font-size: 0.78rem;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--color-muted);
  font-weight: 600;
}
.formula-vars td:first-child {
  font-family: var(--font-mono);
  font-style: italic;
  width: 6rem;
  color: var(--color-accent);
}

/* 互動計算 iframe ------------------------------------------------------- */
.formula-interactive {
  margin: 2.5rem 0;
  background: oklch(97% 0 0);
  border: 1px solid var(--color-line);
  border-radius: 0.5rem;
  overflow: hidden;
}
.formula-interactive-head {
  padding: 0.75rem 1rem;
  border-bottom: 1px solid var(--color-line);
  background: oklch(98% 0 0);
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap;
  gap: 0.5rem;
}
.formula-interactive-title {
  font-family: var(--font-mono);
  font-size: 0.875rem;
  letter-spacing: 0.08em;
  color: var(--color-ink);
  text-transform: uppercase;
}
.formula-interactive-link {
  font-family: var(--font-mono);
  font-size: 0.8125rem;
  color: var(--color-accent);
  text-decoration: none;
  border-bottom: 1px solid transparent;
  transition: border-color var(--duration) var(--ease);
}
.formula-interactive-link:hover { border-bottom-color: var(--color-accent); }
.formula-interactive iframe {
  width: 100%;
  height: 600px;
  border: 0;
  display: block;
  background: var(--color-bg);
}

/* 警示框（常見錯誤）---------------------------------------------------- */
.formula-callout {
  margin: 1.5rem 0;
  padding: 1rem 1.25rem;
  background: oklch(97% 0.02 60);
  border-left: 3px solid oklch(70% 0.16 60);
  border-radius: 0.25rem;
  font-size: 0.95rem;
}
.formula-callout-title {
  font-family: var(--font-mono);
  font-size: 0.8125rem;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: oklch(45% 0.14 60);
  margin-bottom: 0.4rem;
}

/* 延伸閱讀 -------------------------------------------------------------- */
.formula-related {
  margin: 2rem 0;
  padding: 1.25rem 1.5rem;
  background: oklch(98% 0 0);
  border-radius: 0.5rem;
  font-size: 0.95rem;
}
.formula-related-title {
  font-family: var(--font-mono);
  font-size: 0.8125rem;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--color-muted);
  margin-bottom: 0.6rem;
}
.formula-related ul {
  list-style: none;
  margin: 0;
  padding: 0;
}
.formula-related li {
  margin: 0.3rem 0;
}
.formula-related a {
  color: var(--color-ink);
  text-decoration: none;
  border-bottom: 1px solid var(--color-line);
}
.formula-related a:hover {
  border-bottom-color: var(--color-accent);
  color: var(--color-accent);
}

/* Index 頁面：公式卡片 grid ------------------------------------------- */
.formula-grid {
  list-style: none;
  margin: 2rem 0;
  padding: 0;
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(16rem, 1fr));
  gap: 0.75rem;
}
.formula-card {
  padding: 1rem 1.1rem;
  background: oklch(99% 0 0);
  border: 1px solid var(--color-line);
  border-radius: 0.5rem;
  transition: border-color var(--duration) var(--ease),
              transform var(--duration) var(--ease);
}
.formula-card:hover {
  border-color: var(--color-accent);
  transform: translateY(-2px);
}
.formula-card.is-placeholder {
  opacity: 0.55;
  background: oklch(97% 0 0);
}
.formula-card a {
  text-decoration: none;
  color: var(--color-ink);
  display: block;
}
.formula-card-id {
  font-family: var(--font-mono);
  font-size: 0.75rem;
  color: var(--color-muted);
  letter-spacing: 0.08em;
}
.formula-card-name {
  font-weight: 600;
  margin: 0.3rem 0;
  font-size: 1.0625rem;
}
.formula-card-expr {
  font-family: var(--font-mono);
  font-size: 0.85rem;
  color: var(--color-accent);
  font-style: italic;
}

.formula-category {
  margin: 3rem 0 1rem;
}
.formula-category-head {
  display: flex;
  align-items: baseline;
  gap: 0.75rem;
  border-bottom: 2px solid var(--color-ink);
  padding-bottom: 0.4rem;
  margin-bottom: 0.5rem;
}
.formula-category-name {
  font-size: 1.5rem;
  font-weight: 700;
}
.formula-category-count {
  font-family: var(--font-mono);
  font-size: 0.875rem;
  color: var(--color-muted);
}