fix: add focus-within psudo-class

packages/application-extension/style/base.css

@@ -13,7 +13,7 @@
   top: -100em;
 }
 
-.jp-skiplink--focus {
+.jp-skiplink:focus-within {
   position: absolute;
   z-index: 10000;
   top: 0;
@@ -27,7 +27,7 @@
   text-align: center;
 }
 
-.jp-skiplink--focus a {
+.jp-skiplink:focus-within a {
   text-decoration: underline;
   color: var(--jp-content-link-color);
 }