static get styles() {
    return [
      css`
        :host {
          display: block;
        }

        :host ::slotted([slot='content']) {
          overflow: hidden;
        }
      `,
    ];
  }
`LionCollapsible` is a class for custom collapsible element (`<lion-collapsible>` web component).

@customElement lion-collapsible
@extends LitElement