.app-header {
  position: sticky;
  top: 0;
  z-index: var(--z-sticky);
  height: 56px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0 var(--space-6);
  background: var(--color-surface);
  border-bottom: 1px solid var(--color-border);
  gap: var(--space-4);
}

.app-header__logo {
  display: inline-flex;
  align-items: center;
  font-size: var(--text-lg);
  font-weight: var(--font-bold);
  letter-spacing: 0.08em;
  text-transform: uppercase;
  text-decoration: none;
  /* MVP cyber-graphite gradient wordmark (clipped to the text glyphs) */
  background: linear-gradient(135deg, #7C5CFF, #00E0FF);
  -webkit-background-clip: text;
  background-clip: text;
  -webkit-text-fill-color: transparent;
  color: transparent;
  transition: opacity var(--transition-fast);
}
.app-header__logo:hover { opacity: 0.85; }

/* Day mode: deeper cyan end-stop (matches MVP) */
[data-mode="day"] .app-header__logo {
  background: linear-gradient(135deg, #7C5CFF, #00B8D4);
  -webkit-background-clip: text;
  background-clip: text;
}

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

.theme-toggle {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 36px;
  height: 36px;
  border-radius: var(--radius-md);
  color: var(--color-text-secondary);
  background: transparent;
  transition: background var(--transition-fast), color var(--transition-fast);
}
.theme-toggle:hover {
  background: var(--color-surface-2);
  color: var(--color-text-primary);
}
.theme-toggle svg { width: 18px; height: 18px; }