Use the `close-others` attribute to only have one accordion open at a time.

```html
<sd-accordion-group close-others>
  <sd-accordion summary="Accordion 1">
    <p>
      Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nibh justo ullamcorper odio tempor molestie phasellus dui
      vel id. Velit in sed
    </p>
  </sd-accordion>
  <sd-accordion summary="Accordion 2">
    <p>
      Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nibh justo ullamcorper odio tempor molestie phasellus dui
      vel id. Velit in sed
    </p>
  </sd-accordion>
  <sd-accordion summary="Accordion 3">
    <p>
      Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nibh justo ullamcorper odio tempor molestie phasellus dui
      vel id. Velit in sed
    </p>
  </sd-accordion>
</sd-accordion-group>
```