.collapsible:not(:defined),.collapsible:not(:defined) *{opacity:0}.collapsible:defined{opacity:1;transition:opacity .1s}.collapsible::part(base){border:1px solid #ccc;border-radius:4px}.collapsible::part(header){padding:16px}.collapsible::part(summary-icon){rotate:none}.collapsible::part(content){padding:0 16px 16px}.collapsible-content>:first-child{margin-top:0}.collapsible-content>:last-child{margin-bottom:0}