docs: Add visual indication on external links in code reference

Author: pawamoy

docs/css/mkdocstrings.css

@@ -4,3 +4,20 @@ div.doc-contents:not(.first) {
  border-left: 4px solid rgba(230, 230, 230);
  margin-bottom: 80px;
 }
+
+/* Mark external links as such */
+a.autorefs-external:hover::after {
+ /* https://primer.style/octicons/arrow-up-right-24 */
+ background-image: url('data:image/svg+xml,<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><path fill="rgb(0, 0, 0)" d="M18.25 15.5a.75.75 0 00.75-.75v-9a.75.75 0 00-.75-.75h-9a.75.75 0 000 1.5h7.19L6.22 16.72a.75.75 0 101.06 1.06L17.5 7.56v7.19c0 .414.336.75.75.75z"></path></svg>');
+ content: ' ';
+
+ display: inline-block;
+ position: absolute;
+ margin-left: 0.2em;
+ margin-top: 0.4em;
+
+ height: 1em;
+ width: 1em;
+ border-radius: 100%;
+ background-color: var(--md-accent-fg-color);
+}