message: affix copyButton so that it doesn't get scrolled horizontally
diff: @@ -392,6 +392,7 @@ limitations under the License.
  overflow-x: overlay;
  overflow-y: visible;
  max-height: 30vh;
  + position: static;
  }
  .mx_EventTile_content .markdown-body code {
  @@ -406,7 +407,7 @@ limitations under the License.
  visibility: hidden;
  cursor: pointer;
  top: 6px;
  - right: 6px;
  + right: 36px;
  width: 19px;
  height: 19px;
  background-image: url($copy-button-url);
  