accordions-dropdowns（手风琴下拉菜单）

Accordion & Dropdown Animation Principles

Apply Disney's 12 principles to expand/collapse elements for smooth, informative reveals.

Principles Applied to Accordions

1. Squash & Stretch

Content can slightly compress as it collapses, stretch as it expands. Trigger header can squash on click feedback.

2. Anticipation

Before expanding, header briefly depresses. Chevron starts rotation before content reveals. Builds expectation.

3. Staging

Expanded section should be clearly visible. Consider dimming other accordion items. Active header stays highlighted.

4. Straight Ahead & Pose to Pose

Define clear states: collapsed, expanding, expanded, collapsing. Pose-to-pose for controlled, reversible animations.

5. Follow Through & Overlapping Action

Container expands first, content fades in 50-100ms later. Chevron rotation can overshoot and settle. Creates depth.

6. Ease In & Ease Out

Expand: ease-out (fast start, smooth finish). Collapse: ease-in (slow start, fast finish). cubic-bezier(0.4, 0, 0.2, 1) works well.

7. Arcs

Chevron rotation should ease through the arc. Content items can enter with slight arc paths rather than straight down.

8. Secondary Action

While content reveals (primary), chevron rotates (secondary), sibling accordions may collapse (tertiary).

9. Timing

• Expand/collapse: 250-350ms
• Chevron rotation: 200-250ms
• Content fade: 150-200ms
• Stagger internal items: 30-50ms
• Click feedback: 50ms

10. Exaggeration

Important reveals can use more dramatic timing. FAQ accordions can have snappier animations. Match content importance.

11. Solid Drawing

Maintain consistent header heights. Content should not jitter during height animation. Use proper height techniques.

12. Appeal

Smooth accordions feel polished. Janky height animations feel broken. Proper expand/collapse is worth the technical investment.

CSS Implementation

.accordion-content {
  display: grid;
  grid-template-rows: 0fr;
  transition: grid-template-rows 300ms ease-out;
}

.accordion-content.open {
  grid-template-rows: 1fr;
}

.accordion-inner {
  overflow: hidden;
}

.accordion-chevron {
  transition: transform 250ms ease-out;
}

.accordion-header[aria-expanded="true"] .accordion-chevron {
  transform: rotate(180deg);
}

/* Alternative: animate max-height */
.dropdown-content {
  max-height: 0;
  overflow: hidden;
  transition: max-height 300ms ease-out;
}

.dropdown-content.open {
  max-height: 500px; /* larger than content */
}

Key Properties

• grid-template-rows: smooth height
• max-height: simpler but less precise
• transform: rotate chevrons
• opacity: content fade
• overflow: hidden during transition