message: use theme var for bg color
diff: @@ -16,7 +16,7 @@ limitations under the License.
  .mx_MessageEditor {
  border-radius: 4px;
  - background-color: #f3f8fd;
  + background-color: $header-panel-bg-color;
  padding: 11px 13px 7px 56px;
  .mx_MessageEditor_editor {
  