/* ── Topic header ─────────────────────────────────────── */
.topic-header {
  margin-bottom: 44px;
  padding-bottom: 28px;
  border-bottom: 1px solid var(--border);
}

.topic-header__back {
  display: inline-flex;
  align-items: center;
  gap: 5px;
  color: var(--text-muted);
  font-size: 0.83rem;
  margin-bottom: 20px;
  transition: color var(--transition);
}

.topic-header__back::before { content: '\2190'; margin-right: 4px; }

.topic-header__back:hover {
  color: var(--accent);
  text-decoration: none;
}

.topic-header__title {
  font-size: 2rem;
  font-weight: 700;
  color: var(--text);
  line-height: 1.2;
  letter-spacing: -0.025em;
  margin-bottom: 10px;
}

.topic-header__desc {
  font-size: 1rem;
  color: var(--text-secondary);
  line-height: 1.65;
}

/* ── Section layout ───────────────────────────────────── */
.theory-section {
  margin-bottom: 60px;
}

.theory-section__heading {
  font-size: 0.7rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--text-muted);
  margin-bottom: 28px;
}

/* ── Blocks ───────────────────────────────────────────── */
.theory-block { margin-bottom: 22px; }

/* Heading */
.theory-block--heading {
  font-size: 1.2rem;
  font-weight: 600;
  color: var(--text);
  margin-top: 44px;
  margin-bottom: 18px;
  line-height: 1.35;
}

/* Text */
.theory-block--text p {
  font-size: 1rem;
  color: var(--text);
  line-height: 1.8;
}

.theory-block--text p + p { margin-top: 14px; }

/* Note */
.theory-block--note {
  background: var(--accent-bg);
  border-left: 3px solid var(--accent);
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
  padding: 14px 18px;
  display: flex;
  gap: 12px;
  align-items: flex-start;
}

.theory-block--note .note__prefix {
  font-size: 0.65rem;
  font-weight: 700;
  letter-spacing: 0.07em;
  text-transform: uppercase;
  background: var(--accent);
  color: #fff;
  padding: 2px 7px;
  border-radius: 3px;
  margin-top: 2px;
  flex-shrink: 0;
}

.theory-block--note .note__text {
  font-size: 0.9rem;
  color: var(--text);
  line-height: 1.7;
}

/* Hood */
.theory-block--hood {
  background: #fffbeb;
  border-left: 3px solid #f59e0b;
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
  padding: 14px 18px;
}

.hood__header {
  display: flex;
  align-items: center;
  gap: 10px;
  margin-bottom: 8px;
}

.hood__prefix {
  font-size: 0.65rem;
  font-weight: 700;
  letter-spacing: 0.07em;
  text-transform: uppercase;
  background: #d97706;
  color: #fff;
  padding: 2px 7px;
  border-radius: 3px;
  white-space: nowrap;
  flex-shrink: 0;
}

.hood__title {
  font-size: 0.88rem;
  font-weight: 600;
  color: #92400e;
}

.hood__text {
  font-size: 0.9rem;
  color: #78350f;
  line-height: 1.8;
}

/* ── Code block ───────────────────────────────────────── */
.code-block {
  background: var(--surface);
  border: 1px solid var(--code-border);
  border-radius: var(--radius-sm);
  overflow: hidden;
}

.code-block__header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 8px 14px;
  background: var(--code-bg);
  border-bottom: 1px solid var(--code-border);
}

.code-block__title {
  font-size: 0.8rem;
  font-weight: 500;
  color: var(--text-secondary);
}

.code-block__actions {
  display: flex;
  align-items: center;
  gap: 8px;
}

.code-block__lang {
  font-size: 0.68rem;
  color: var(--text-muted);
  font-family: var(--font-mono);
  background: var(--surface-3);
  padding: 2px 7px;
  border-radius: 3px;
}

.code-block__copy {
  background: none;
  border: 1px solid var(--border);
  color: var(--text-secondary);
  font-family: var(--font-ui);
  font-size: 0.75rem;
  padding: 2px 10px;
  border-radius: var(--radius-xs);
  cursor: pointer;
  transition: all var(--transition);
}

.code-block__copy:hover {
  border-color: var(--accent-border);
  color: var(--accent);
  background: var(--accent-bg);
}

.code-block__copy.copied {
  border-color: var(--easy-border);
  color: var(--success);
  background: var(--success-bg);
}

.code-block__pre {
  margin: 0;
  padding: 18px 20px;
  overflow-x: auto;
  background: var(--code-bg);
}

.code-block__pre code {
  font-family: var(--font-mono) !important;
  font-size: 0.875rem;
  line-height: 1.75;
  background: none !important;
  padding: 0 !important;
  text-shadow: none !important;
}

.code-block__explanation {
  padding: 12px 16px;
  background: var(--surface);
  border-top: 1px solid var(--code-border);
  font-size: 0.875rem;
  color: var(--text-secondary);
  line-height: 1.65;
}

/* ── Topic navigation ────────────────────────────────── */
.topic-nav {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-top: 56px;
  padding-top: 24px;
  border-top: 1px solid var(--border);
  gap: 16px;
}

.topic-nav__btn {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 10px 18px;
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  font-size: 0.875rem;
  font-weight: 500;
  color: var(--text-secondary);
  text-decoration: none;
  transition: border-color var(--transition), color var(--transition), background var(--transition);
  max-width: 48%;
}

.topic-nav__btn:hover {
  border-color: var(--accent-border);
  color: var(--accent);
  background: var(--accent-bg);
  text-decoration: none;
}

.topic-nav__btn--prev {
  text-align: left;
}

.topic-nav__btn--next {
  text-align: right;
  margin-left: auto;
}

/* ── Mobile base ─────────────────────────────────────── */
.topic-header__title { font-size: 1.35rem; }
.topic-header__desc { font-size: 0.9rem; }

.code-block__pre { padding: 14px; }
.code-block__pre code { font-size: 0.8rem; }
.code-block__header { padding: 7px 12px; }

.topic-nav { flex-direction: column; gap: 10px; }
.topic-nav__btn { max-width: 100%; }
.topic-nav__btn--next { margin-left: 0; }

/* ── Tablet ──────────────────────────────────────────── */
@media (min-width: 601px) {
  .topic-header__title { font-size: 1.6rem; }
  .topic-header__desc { font-size: 0.95rem; }

  .code-block__pre { padding: 18px 20px; }
  .code-block__pre code { font-size: 0.875rem; }
}

/* ── Desktop ─────────────────────────────────────────── */
@media (min-width: 901px) {
  .content-inner { max-width: var(--content-max); }
  .topic-header__title { font-size: 2rem; }
  .topic-header__desc { font-size: 1rem; }

  .topic-nav { flex-direction: row; }
  .topic-nav__btn { max-width: 48%; }
  .topic-nav__btn--next { margin-left: auto; }
}

/* ── Terminal variant ─────────────────────────────────── */
.code-block--terminal .code-block__header {
  background: #1c2128;
  border-bottom-color: #30363d;
}

.code-block--terminal .code-block__title { color: #8b949e; }

.code-block--terminal .code-block__lang {
  background: #30363d;
  color: var(--terminal-green);
  border: none;
}

.code-block--terminal .code-block__copy {
  border-color: #30363d;
  color: #8b949e;
}

.code-block--terminal .code-block__copy:hover {
  border-color: var(--terminal-green);
  color: var(--terminal-green);
  background: rgba(63,185,80,0.08);
}

.code-block--terminal .code-block__pre {
  background: var(--terminal-bg);
}

.code-block--terminal .code-block__pre code {
  color: var(--terminal-text) !important;
}

.code-block--terminal .code-block__explanation {
  background: #161b22;
  border-top-color: #30363d;
  color: #8b949e;
}