Extend the default collapse behaviour to create an accordion.

<div>   
   <b-button v-b-toggle.collapse-1 variant="primary">Toggle Collapse</b-button>   
   <b-collapse id="collapse-1" class="mt-2">    
      <b-card>       
         <p class="card-text">Collapse contents Here</p>       
         <b-button v-b-toggle.collapse-1-inner size="sm">Toggle Inner Collapse</b-button>       
         <b-collapse id="collapse-1-inner" class="mt-2">         
            <b-card>Hello!</b-card>       
         </b-collapse>     
      </b-card>   
   </b-collapse> 
</div>

You can check some other layouts of collapse below. For adding any of the below layout in the template, please check their relative code in the src -> views -> ui-elements-> Accordions.vue folder.