Demo and API docs

<iron-collapse>

iron-collapse creates a collapsible block of content. By default, the content will be collapsed. Use opened or toggle() to show/hide the content. The aria-expanded attribute should only be set on the button that controls the collapsable area, not on the area itself. See https://www.w3.org/WAI/GL/wiki/Using_aria-expanded_to_indicate_the_state_of_a_collapsible_element#Description

<button id="button" on-click="toggle">toggle collapse</button>

<iron-collapse id="collapse">
  <div>Content goes here...</div>
</iron-collapse>

...

toggle: function() {
  this.$.collapse.toggle();
  this.$.button.setAttribute('aria-expanded', this.$.collapse.opened);
}

iron-collapse adjusts the max-height/max-width of the collapsible element to show/hide the content. So avoid putting padding/margin/border on the collapsible directly, and instead put a div inside and style that.

<style>
  .collapse-content {
    padding: 15px;
    border: 1px solid #dedede;
  }
</style>

<iron-collapse>
  <div class="collapse-content">
    <div>Content goes here...</div>
  </div>
</iron-collapse>

Styling

The following custom properties and mixins are available for styling:

Custom property	Description	Default
--iron-collapse-transition-duration	Animation transition duration	300ms