/* App-Shell: Header, Sidebar, Hauptbereich, Footer. */

.app-header {
  position: sticky;
  top: 0;
  z-index: var(--z-header);
  background: var(--color-surface);
  border-bottom: 1px solid var(--color-border);
}

.app-header__inner {
  display: flex;
  align-items: center;
  gap: var(--space-5);
  padding: var(--space-3) var(--space-5);
  min-height: var(--header-height);
  flex-wrap: wrap;
}

.app-header__brand {
  display: flex;
  flex-direction: column;
  text-decoration: none;
  color: inherit;
  flex-shrink: 0;
}

.app-header__eyebrow {
  font-size: var(--font-size-xs);
  text-transform: uppercase;
  letter-spacing: 0.09em;
  color: var(--color-text-muted);
}

.app-header__title {
  font-size: var(--font-size-lg);
  font-weight: 650;
  letter-spacing: -0.015em;
}

.chapter-nav {
  display: flex;
  gap: var(--space-2);
  flex-wrap: wrap;
  margin-left: auto;
}

.app-body {
  display: grid;
  grid-template-columns: var(--sidebar-width) minmax(0, 1fr);
  align-items: start;
  flex: 1;
}

.sidebar {
  position: sticky;
  top: var(--header-height);
  z-index: var(--z-sidebar);
  align-self: start;
  max-height: calc(100vh - var(--header-height));
  overflow-y: auto;
  padding: var(--space-5) var(--space-4);
  border-right: 1px solid var(--color-border);
  background: var(--color-surface);
}

.app-main {
  padding: var(--space-6) var(--space-6) var(--space-8);
  min-width: 0;
}

.app-main:focus {
  outline: none;
}

.section {
  max-width: var(--content-max);
  margin: 0 auto;
  animation: section-in var(--transition-base);
}

@keyframes section-in {
  from { opacity: 0; transform: translateY(6px); }
  to { opacity: 1; transform: none; }
}

@media (prefers-reduced-motion: reduce) {
  .section { animation: none; }
}

.app-footer {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--space-4);
  flex-wrap: wrap;
  padding: var(--space-4) var(--space-6);
  border-top: 1px solid var(--color-border);
  background: var(--color-surface);
  color: var(--color-text-muted);
  font-size: var(--font-size-sm);
}

.app-footer p { margin: 0; }

.app-footer__meta { font-size: var(--font-size-xs); }

.nav-toggle {
  display: none;
  align-items: center;
  gap: var(--space-2);
  padding: var(--space-2) var(--space-3);
  background: var(--color-surface);
  border: 1px solid var(--color-border-strong);
  border-radius: var(--radius-md);
  cursor: pointer;
  font-size: var(--font-size-sm);
}

.nav-toggle__bars,
.nav-toggle__bars::before,
.nav-toggle__bars::after {
  display: block;
  width: 16px;
  height: 2px;
  background: currentColor;
  content: "";
}

.nav-toggle__bars {
  position: relative;
}

.nav-toggle__bars::before { position: absolute; top: -5px; }
.nav-toggle__bars::after { position: absolute; top: 5px; }

/* Tablet und schmaler: Sidebar wird einklappbar */
@media (max-width: 900px) {
  .app-body {
    grid-template-columns: minmax(0, 1fr);
  }

  .nav-toggle {
    display: inline-flex;
  }

  .chapter-nav {
    order: 3;
    width: 100%;
    margin-left: 0;
  }

  .sidebar {
    position: static;
    max-height: none;
    border-right: none;
    border-bottom: 1px solid var(--color-border);
  }

  .sidebar[hidden] {
    display: none;
  }

  .app-main {
    padding: var(--space-5) var(--space-4) var(--space-7);
  }
}

@media (max-width: 640px) {
  .app-header__inner {
    padding: var(--space-3) var(--space-4);
    gap: var(--space-3);
  }

  .app-header__title {
    font-size: var(--font-size-base);
  }
}