Change the ExternalAnchor to accept a direct class prop instead of extras.

source/ts/components/external-anchor.ts

@@ -1,18 +1,21 @@
 import {html, Component} from 'htm/preact';
 
 type Props = {
-  extra?: Record<string, string>;
+  class?: string;
   text: string;
   url: string;
 };
 
 export default class ExternalAnchor extends Component<Props> {
   render() {
-    const {extra, text, url} = this.props;
-
     return html`
-      <a href="${url}" target="_blank" rel="noopener noreferrer" ...${extra}>
-        ${text}
+      <a
+        class="${this.props.class}"
+        href="${this.props.url}"
+        rel="noopener noreferrer"
+        target="_blank"
+      >
+        ${this.props.text}
       </a>
     `;
   }