body {
  margin: 0;
  font-family: Inter, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  background: #f3f5f8;
  color: #102040;
  display: flex;
  flex-direction: column;
  min-height: 100dvh;
}

/* ── Header ───────────────────────────────────────────── */
.page-header {
  position: sticky;
  top: 0;
  overflow: visible;
  z-index: 30;
  height: var(--header-height);
  box-sizing: border-box;
  display: flex;
  align-items: center;
  justify-content: flex-start;
  gap: 16px;
  padding: 0 24px;
  background: #ffffffee;
  backdrop-filter: blur(8px);
  border-bottom: 1px solid #d7e1eb;
  user-select: none;
  flex-shrink: 0;
}

.app-logo {
  height: 36px;
  width: auto;
  object-fit: contain;
  user-select: none;
  transition: filter 0.3s ease;
}

[data-theme="dark"]   .app-logo,
[data-theme="aurora"] .app-logo,
[data-theme="grey"]   .app-logo {
  filter: drop-shadow(0 0 6px rgba(120, 200, 255, 1))
          drop-shadow(0 0 16px rgba(80, 160, 255, 0.85))
          drop-shadow(0 0 32px rgba(60, 130, 255, 0.5));
}

.menu-button:focus:not(:focus-visible) {
  outline: none;
}

/* ── Page layout row (sidebar + main) ─────────────────── */
#page-layout {
  flex: 1;
  display: flex;
  flex-direction: row;
  align-items: stretch;
  min-height: calc(100dvh - var(--header-height));
}

main.hero {
  flex: 1;
  min-width: 0;
  display: flex;
  flex-direction: column;
  overflow: hidden;
  height: calc(100dvh - var(--header-height, 76px));
}

.hero-screens-row {
  flex: 1;
  min-height: 0;
  display: flex;
  flex-direction: row;
  overflow: hidden;
}

/* ── Hero screens ─────────────────────────────────────── */
.hero-screen {
  flex: 1 1 0;
  display: flex;
  flex-direction: column;
  overflow: hidden;
  min-width: 0;
  border-right: 1px solid var(--border, #e2e8f0);
  background: var(--surface, #ffffff);
}

.hero-screen:last-child { border-right: none; }

[data-theme="dark"] .page-header { background: rgba(1,4,9,0.88); backdrop-filter: blur(12px); border-bottom-color: #30363d; }
[data-theme="grey"] .page-header { background: rgba(13,17,23,0.88); backdrop-filter: blur(12px); border-bottom-color: #444c56; }

[data-theme="dark"] .hero-screen { background: var(--bg); border-right-color: rgba(255,255,255,0.05); }
[data-theme="grey"] .hero-screen { background: var(--bg); border-right-color: rgba(255,255,255,0.05); }
[data-theme="grey"] .app-logo {
  filter: drop-shadow(0 0 6px rgba(87,171,90,0.55))
          drop-shadow(0 0 16px rgba(87,171,90,0.35));
}

.hero-copy {
  max-width: 760px;
  margin: 24px auto 0;
  padding: 0 24px 32px;
  text-align: center;
}

.hero-copy h2 {
  margin: 0 0 12px;
  font-size: clamp(2rem, 3vw, 3rem);
}

.hero-copy p {
  margin: 0;
  color: #425366;
  font-size: 1rem;
}

/* ── Prose & cards ────────────────────────────────────── */
p {
  max-width: 760px;
  margin: 20px auto;
  padding: 0 24px;
  line-height: 1.75;
}

.card,
.math-block {
  max-width: 760px;
  margin: 20px auto;
  padding: 20px;
  background: #ffffff;
  border: 1px solid #d7e1eb;
  border-radius: 18px;
  box-shadow: 0 16px 40px rgba(15, 32, 64, 0.07);
}

.code-block {
  width: 100%;
  box-sizing: border-box;
  overflow-x: auto;
  font-family: SFMono-Regular, Menlo, Monaco, Consolas, "Liberation Mono", "Courier New", monospace;
  font-size: 0.95rem;
  background: #f8fafc;
  padding: 14px;
  border-radius: 12px;
  margin: 0;
}

/* ── Mobile ───────────────────────────────────────────── */
@media (max-width: 768px) {
  .page-header {
    padding: 0 12px;
    gap: 8px;
  }
}

@media (max-width: 640px) {
  .card,
  .math-block {
    margin: 12px 0;
    padding: 14px;
    border-radius: 12px;
    box-shadow: 0 4px 16px rgba(15, 32, 64, 0.06);
  }

  .card h2 {
    font-size: 1rem;
    margin-bottom: 10px;
  }

  .content-title {
    font-size: 1.4rem;
    margin: 0 0 16px;
  }

  .code-block {
    font-size: 0.8rem;
    padding: 10px 12px;
    border-radius: 8px;
  }
}

.math-block .expression {
  font-size: 1.1rem;
  line-height: 1.9;
}

:root {
  --header-height: 76px;
  --screen-header-h: 65px;
}

/* ── Fullscreen toggle button ─────────────────────────── */
/* ── Fullscreen toggle button (lives in .page-header) ─── */
.dp-fullscreen-btn {
  margin-left: auto;       /* absorbs the gap, pushes theme-ctrl right */
  flex-shrink: 0;
  width: 32px;
  height: 32px;
  display: flex;
  align-items: center;
  justify-content: center;
  border: none;
  border-radius: 20px;
  background: transparent;
  color: var(--text-muted, #94a3b8);
  cursor: pointer;
  transition: background 0.15s, color 0.15s, transform 0.15s;
}
.dp-fullscreen-btn:hover  { background: rgba(0,0,0,0.055); color: var(--text, #102040); transform: scale(1.08); }

/* theme-controller no longer needs its own auto-margin once the sibling is present */
.dp-fullscreen-btn ~ .theme-controller { margin-left: 0; }

/* ── Fullscreen exit hint toast ───────────────────────── */
.dp-fs-toast {
  position: fixed;
  top: 18px;
  left: 50%;
  transform: translateX(-50%) translateY(0);
  z-index: 9999;
  background: rgba(18, 18, 22, 0.78);
  backdrop-filter: blur(10px);
  -webkit-backdrop-filter: blur(10px);
  color: rgba(230, 230, 240, 0.92);
  font-size: 0.72rem;
  font-family: var(--code-font, "JetBrains Mono", monospace);
  letter-spacing: 0.02em;
  padding: 7px 16px;
  border-radius: 8px;
  border: 1px solid rgba(255,255,255,0.1);
  pointer-events: none;
  white-space: nowrap;
  animation: dp-toast-in 0.22s cubic-bezier(0.34, 1.56, 0.64, 1) both;
}
.dp-fs-toast kbd {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  margin-left: 6px;
  padding: 1px 7px;
  border: 1.5px solid rgba(255,255,255,0.35);
  border-bottom-width: 2.5px;
  border-radius: 4px;
  background: rgba(255,255,255,0.08);
  font-family: inherit;
  font-size: 0.68rem;
  font-weight: 600;
  color: #ffffff;
  letter-spacing: 0.04em;
}
.dp-fs-toast--out {
  animation: dp-toast-out 0.38s ease forwards;
}
@keyframes dp-toast-in {
  from { opacity: 0; transform: translateX(-50%) translateY(-10px); }
  to   { opacity: 1; transform: translateX(-50%) translateY(0); }
}
@keyframes dp-toast-out {
  from { opacity: 1; transform: translateX(-50%) translateY(0); }
  to   { opacity: 0; transform: translateX(-50%) translateY(-6px); }
}

/* ── Fullscreen mode ──────────────────────────────────── */
body.dp-fullscreen { --header-height: 0px; }
body.dp-fullscreen .page-header {
  height: 0;
  padding: 0;
  border: none;
  overflow: hidden;
  pointer-events: none;
}
body.dp-fullscreen .nav-sidebar {
  width: 0 !important;
  opacity: 0;
  pointer-events: none;
}