Move display:flex from outer div to ButtonGroup ul

ts/editor-toolbar/ButtonGroup.svelte

@@ -10,7 +10,10 @@
 
 <style lang="scss">
     ul {
-        display: inline-block;
+        display: flex;
+        /* flex-flow: nowrap for a scrollable toolbar */
+        flex-flow: wrap;
+        overflow: scroll;
 
         padding-inline-start: 0;
         margin-bottom: 0;

ts/editor-toolbar/EditorToolbar.svelte

@@ -10,14 +10,10 @@
 
 <style lang="scss">
     div {
-        display: flex;
-        flex-wrap: wrap;
-
         position: sticky;
         top: 0;
         left: 0;
-        z-index: 5;
-        padding: 2px;
+        z-index: 10;
 
         background: var(--bg-color);
         border-bottom: 1px solid var(--border);