Fix search not being easily findable on smaller screens in web UI (#25576)

app/javascript/styles/mastodon/components.scss

@@ -133,12 +133,13 @@
     color: $darker-text-color;
     background: transparent;
     padding: 6px 17px;
-    border: 1px solid $ui-primary-color;
+    border: 1px solid lighten($ui-base-color, 12%);
 
     &:active,
     &:focus,
     &:hover {
-      border-color: lighten($ui-primary-color, 4%);
+      background: lighten($ui-base-color, 4%);
+      border-color: lighten($ui-base-color, 16%);
       color: lighten($darker-text-color, 4%);
       text-decoration: none;
     }