app/javascript/flavours/glitch/styles/admin.scss

@@ -1683,10 +1683,11 @@ a.sparkline {
 
   a {
     color: $highlight-text-color;
-    text-decoration: none;
 
-    &:hover {
+    &:hover,
-      text-decoration: underline;
+    &:active,
+    &:focus {
+      text-decoration: none;
     }
   }
 

app/javascript/styles/mastodon/admin.scss

@@ -1681,15 +1681,6 @@ a.sparkline {
   box-sizing: border-box;
   min-height: 100%;
 
-  a {
-    color: $highlight-text-color;
-    text-decoration: none;
-
-    &:hover {
-      text-decoration: underline;
-    }
-  }
-
   p {
     margin-bottom: 20px;
     unicode-bidi: plaintext;