chrome/browser/resources/settings/site_favicon.html

    <style>
      :host {
        --site-favicon-height: 16px;
        --site-favicon-width: 16px;
      }

      #favicon {
        background-repeat: no-repeat;
        background-size: contain;
        border-radius: inherit;
        display: block;
        height: var(--site-favicon-height);
        width: var(--site-favicon-width);
      }
    </style>
    <div
        id="favicon"
        style="background-image: [[getBackgroundImage_(faviconUrl, url)]]">
    </div>