Fix show Tinymce style formats (#18305)

Because we upgraded to version 5:
https://github.com/directus/directus/pull/18107
And there's a breaking change:
https://github.com/tinymce/tinymce/blob/develop/modules/tinymce/CHANGELOG.md#:~:text=Renamed%20the%20styleselect%20toolbar%20button%20and%20formats%20menu%20item%20to%20styles.%20%23TINY%2D8328

app/src/interfaces/input-rich-text-html/input-rich-text-html.vue

@@ -364,7 +364,7 @@ export default defineComponent({
 				.join(' ');
 
 			if (styleFormats) {
-				toolbarString += ' styleselect';
+				toolbarString += ' styles';
 			}
 
 			return {

app/src/interfaces/input-rich-text-html/tinymce-overrides.css

@@ -151,6 +151,10 @@ body.dark .tox .tox-toolbar__overflow {
 	background: var(--border-normal);
 }
 
+.tox .tox-tbtn--bespoke {
+	background: inherit;
+}
+
 .tox .tox-tbtn + .tox .tox-tbtn {
 	margin-left: 2px;
 }