add comments for Todo task of dark mode

src/client/js/components/PageEditor/GridEditModal.jsx

@@ -33,6 +33,7 @@ export default class GridEditModal extends React.PureComponent {
   showBgCols() {
     const cols = [];
     for (let i = 0; i < 12; i++) {
+      // [TODO support dark mode by GW-3037]
       cols.push(<div className="bg-light grid-bg-col col-1"></div>);
     }
     return cols;

src/client/styles/scss/_on-edit.scss

@@ -316,6 +316,7 @@ body.on-edit {
   height: 135px;
 }
 
+// [TODO support dark mode by GW-3037]
 .grid-bg-col {
   border-right: 5px solid white;
   border-left: 5px solid white;