/* ============================================================
   APP SHELL
   ============================================================ */
#app {
  width: 100%;
  height: 100dvh;
  display: flex;
  flex-direction: column;
  overflow: hidden;
  position: relative;
}

.quiz-header {
  position: relative;
  z-index: 10;
  padding: var(--space-4) var(--space-6);
  display: flex;
  align-items: center;
  justify-content: space-between;
  min-height: 56px;
  flex-shrink: 0;
}
.quiz-header.hidden { display: none; }

.header-back {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  color: var(--color-text-muted);
  font-size: var(--text-xs);
  font-weight: 500;
  padding: var(--space-2) var(--space-3);
  border-radius: var(--radius-md);
  transition: color var(--transition-interactive), background var(--transition-interactive);
  min-width: 80px;
}
.header-back:hover { color: var(--color-text); background: var(--color-surface); }
.header-back.invisible { visibility: hidden; pointer-events: none; }

.header-progress {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: var(--space-1);
  flex: 1;
  max-width: 240px;
}
.progress-bar {
  width: 100%;
  height: 3px;
  background: var(--color-surface-2);
  border-radius: var(--radius-full);
  overflow: hidden;
}
.progress-fill {
  height: 100%;
  background: var(--color-primary);
  border-radius: var(--radius-full);
  transition: width 400ms cubic-bezier(0.16, 1, 0.3, 1);
}
.progress-label {
  font-size: var(--text-xs);
  color: var(--color-text-faint);
  font-weight: 500;
}

.header-logo {
  min-width: 80px;
  text-align: right;
  display: flex;
  align-items: center;
  justify-content: flex-end;
}

/* ============================================================
   SCREEN CONTAINER
   ============================================================ */
.screen-container {
  flex: 1;
  position: relative;
  overflow: hidden;
}

.screen {
  position: absolute;
  inset: 0;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  padding: var(--space-6);
  opacity: 0;
  transform: translateX(40px);
  pointer-events: none;
  transition: opacity var(--transition-enter), transform var(--transition-enter);
  overflow-y: auto;
  -webkit-overflow-scrolling: touch;
}
.screen.active {
  opacity: 1;
  transform: translateX(0);
  pointer-events: auto;
}
.screen.exit-left {
  opacity: 0;
  transform: translateX(-40px);
  transition: opacity var(--transition-exit), transform var(--transition-exit);
}
.screen.exit-right {
  opacity: 0;
  transform: translateX(40px);
  transition: opacity var(--transition-exit), transform var(--transition-exit);
}

.screen-inner {
  width: 100%;
  max-width: var(--content-default);
  display: flex;
  flex-direction: column;
  align-items: center;
  text-align: center;
}