Fix markdown anchor icon interaction

CHANGELOG

@@ -16,6 +16,7 @@ v 8.12.0 (unreleased)
   - Fix branches page dropdown sort alignment (ClemMakesApps)
   - Add white background for no readme container (ClemMakesApps)
   - API: Expose issue confidentiality flag. (Robert Schilling)
+  - Fix markdown anchor icon interaction (ClemMakesApps)
   - Optimistic locking for Issues and Merge Requests (title and description overriding prevention)
   - Add `wiki_page_events` to project hook APIs (Ben Boeckel)
   - Remove Gitorious import

app/assets/images/icon_anchor.svg

+<svg xmlns="http://www.w3.org/2000/svg" width="16" height="16" viewBox="0 0 16 16"><path fill="#333" fill-rule="evenodd" d="M9.683 6.676l-.047-.048C8.27 5.26 6.07 5.243 4.726 6.588l-2.29 2.29c-1.344 1.344-1.328 3.544.04 4.91 1.366 1.368 3.564 1.385 4.908.04l1.753-1.752c-.695.074-1.457-.078-2.176-.444L5.934 12.66c-.634.634-1.67.625-2.312-.017-.642-.643-.65-1.677-.017-2.312L6.035 7.9c.634-.634 1.67-.625 2.312.017.024.024.048.05.07.075l.003-.002c.36.36.943.366 1.3.01.355-.356.35-.938-.01-1.3l-.027-.024zM6.58 9.586l.048.05c1.367 1.366 3.565 1.384 4.91.04l2.29-2.292c1.344-1.343 1.328-3.542-.04-4.91-1.366-1.366-3.564-1.384-4.908-.04L7.127 4.187c.695-.074 1.457.078 2.176.444l1.028-1.027c.635-.634 1.67-.624 2.313.017.643.644.652 1.678.018 2.312l-2.43 2.432c-.635.634-1.67.624-2.313-.018-.024-.024-.048-.05-.07-.075l-.003.004c-.36-.362-.943-.367-1.3-.01-.355.355-.35.937.01 1.3.01.007.018.015.027.023z"/></svg>
\ No newline at end of file

app/assets/stylesheets/framework/typography.scss

@@ -159,25 +159,18 @@
     position: relative;
 
     a.anchor {
-      // Setting `display: none` would prevent the anchor being scrolled to, so
-      // instead we set the height to 0 and it gets updated on hover.
-      height: 0;
+      left: -16px;
+      position: absolute;
+      text-decoration: none;
+
+      &:after {
+        content: url('icon_anchor.svg');
+        visibility: hidden;
+      }
     }
 
-    &:hover > a.anchor {
-      $size: 14px;
-      position: absolute;
-      right: 100%;
-      top: 50%;
-      margin-top: -11px;
-      margin-right: 0;
-      padding-right: 15px;
-      display: inline-block;
-      width: $size;
-      height: $size;
-      background-image: image-url("icon-link.png");
-      background-size: contain;
-      background-repeat: no-repeat;
+    &:hover > a.anchor:after {
+      visibility: visible;
     }
   }
 }