/* ============================================================
   LAYOUT — App Shell, Top Bar, Navigation, Content Area
   ============================================================ */

/* ---- App Shell ---- */
#app-shell {
  display: flex;
  flex-direction: column;
  height: 100vh;
  overflow: hidden;
}

/* ---- Top Bar ---- */
#topbar {
  height: var(--topbar-height);
  min-height: var(--topbar-height);
  display: flex;
  align-items: center;
  background: var(--color-topbar-bg);
  border-bottom: 1px solid var(--color-topbar-border);
  padding: 0 var(--space-4);
  gap: var(--space-4);
  z-index: 100;
  position: relative;
  flex-shrink: 0;
}

/* ---- Brand ---- */
.topbar-brand {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  font-weight: var(--font-weight-semibold);
  font-size: var(--font-size-md);
  color: var(--color-topbar-active);
  white-space: nowrap;
  flex-shrink: 0;
  letter-spacing: -0.01em;
}

.topbar-brand svg {
  width: 26px;
  height: 26px;
  flex-shrink: 0;
}

/* ---- Nav Tabs ---- */
#nav-tabs {
  display: flex;
  align-items: center;
  gap: 1px;
  flex: 1;
  overflow-x: auto;
  overflow-y: hidden;
  scrollbar-width: none;
  padding: 0 var(--space-2);
}

#nav-tabs::-webkit-scrollbar {
  display: none;
}

.tab-btn {
  padding: 5px 11px;
  font-size: var(--font-size-sm);
  font-weight: var(--font-weight-medium);
  color: var(--color-topbar-text);
  border-radius: var(--radius-md);
  white-space: nowrap;
  transition: background var(--transition-fast), color var(--transition-fast);
  flex-shrink: 0;
  position: relative;
}

.tab-btn:hover {
  background: var(--color-topbar-hover-bg);
  color: var(--color-topbar-active);
}

.tab-btn.active {
  background: var(--color-topbar-active-bg);
  color: var(--color-topbar-active);
  font-weight: var(--font-weight-semibold);
}

/* Active tab underline accent */
.tab-btn.active::after {
  content: '';
  position: absolute;
  bottom: -5px;
  left: 50%;
  transform: translateX(-50%);
  width: calc(100% - 16px);
  height: 2px;
  background: var(--color-accent);
  border-radius: var(--radius-pill);
}

/* ---- Top Bar Actions ---- */
.topbar-actions {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  flex-shrink: 0;
  margin-left: auto;
}

.icon-btn {
  width: 30px;
  height: 30px;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: var(--radius-md);
  color: var(--color-topbar-text);
  transition: background var(--transition-fast), color var(--transition-fast);
}

.icon-btn:hover {
  background: var(--color-topbar-hover-bg);
  color: var(--color-topbar-active);
}

.user-avatar {
  width: 28px;
  height: 28px;
  border-radius: var(--radius-pill);
  background: var(--color-accent);
  color: var(--color-text-inverse);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: var(--font-size-xs);
  font-weight: var(--font-weight-bold);
  cursor: pointer;
  letter-spacing: 0.02em;
  transition: opacity var(--transition-fast);
}

.user-avatar:hover {
  opacity: 0.88;
}

/* ---- Content Area ---- */
#content-area {
  flex: 1;
  overflow-y: auto;
  overflow-x: hidden;
  background: var(--color-bg);
  padding: var(--content-padding);
}

/* ---- Content Pages ---- */
.content-page {
  display: none;
  max-width: var(--content-max-width);
  margin: 0 auto;
}

.content-page.active {
  display: block;
}