.app-shell {
  display: flex;
  flex-direction: column;
  min-height: 100dvh;
  max-width: 680px;
  margin: 0 auto;
  padding-bottom: 84px; /* Space for mobile bottom nav */
}

.app-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: var(--space-4);
  background-color: var(--bg-surface);
  border-bottom: 1px solid var(--border-color);
  position: sticky;
  top: 0;
  z-index: 20;
}

.header-left {
  display: flex;
  align-items: center;
  gap: var(--space-3);
}

.brand-badge {
  background: var(--color-primary);
  color: #FFFFFF;
  font-weight: 800;
  font-size: 0.85rem;
  letter-spacing: 0.06em;
  padding: var(--space-2) var(--space-3);
  border-radius: var(--radius-sm);
}

.header-title {
  font-size: 1.05rem;
}

.header-subtitle {
  font-size: 0.78rem;
  color: var(--text-muted);
}

.header-right {
  display: flex;
  align-items: center;
  gap: var(--space-2);
}

.avatar-btn {
  width: 40px;
  height: 40px;
  border-radius: var(--radius-pill);
  background: var(--color-primary-soft);
  color: var(--color-primary);
  font-weight: 700;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  text-decoration: none;
  border: 1px solid var(--border-color);
}

.main-content {
  flex: 1;
  padding: var(--space-4);
  display: flex;
  flex-direction: column;
  gap: var(--space-4);
}

/* Mobile Bottom Navigation (Home, Plan, Track, Partner, Profile) */
.app-nav {
  position: fixed;
  bottom: 0;
  left: 0;
  right: 0;
  background-color: var(--bg-surface);
  border-top: 1px solid var(--border-color);
  display: grid;
  grid-template-columns: repeat(5, 1fr);
  padding: var(--space-2) var(--space-2) calc(var(--space-2) + env(safe-area-inset-bottom));
  z-index: 30;
}

.nav-item {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  min-height: 48px;
  border-radius: var(--radius-sm);
  color: var(--text-muted);
  font-size: 0.75rem;
  font-weight: 600;
  gap: 2px;
  text-decoration: none;
  transition: background-color var(--transition-fast), color var(--transition-fast);
}

.nav-item:hover {
  text-decoration: none;
  background-color: var(--bg-subtle);
}

.nav-item.active {
  color: var(--color-primary);
  background-color: var(--color-primary-soft);
}

.nav-icon {
  font-size: 1.15rem;
  line-height: 1;
}

/* Desktop Left Rail Layout */
@media (min-width: 900px) {
  .app-shell {
    max-width: 1040px;
    padding-left: 220px;
    padding-bottom: var(--space-6);
  }

  .app-nav {
    top: 0;
    bottom: 0;
    left: 0;
    right: auto;
    width: 220px;
    display: flex;
    flex-direction: column;
    justify-content: flex-start;
    padding: var(--space-5) var(--space-3);
    gap: var(--space-2);
    border-top: none;
    border-right: 1px solid var(--border-color);
  }

  .nav-item {
    flex-direction: row;
    justify-content: flex-start;
    padding: 0 var(--space-4);
    font-size: 0.95rem;
    gap: var(--space-3);
  }
}