fix markdown placeholder

ui/js/component/formField/view.jsx

@@ -48,6 +48,7 @@ class FormField extends React.PureComponent {
       this._element = SimpleMDE;
       this._type = "textarea";
       this._extraElementProps.options = {
+        placeholder: this.props.placeholder,
         hideIcons: ["guide", "heading", "image", "fullscreen", "side-by-side"],
       };
     } else if (formFieldFileSelectorTypes.includes(this.props.type)) {

ui/js/component/publishForm/view.jsx

@@ -584,12 +584,11 @@ class PublishForm extends React.PureComponent {
                       }}
                     />
                   </div>
-                  <div className="card__content">
-                    <h4>{__("Description")}</h4>
-                  </div>
+                  <div className="card__content" />
                   <div className="card__content">
                     <FormRow
                       type="SimpleMDE"
+                      label={__("Description")}
                       ref="meta_description"
                       name="description"
                       value={this.state.meta_description}

ui/scss/component/_tabs.scss

@@ -6,6 +6,7 @@ nav.sub-header
   max-width: $width-page-constrained;
   margin-bottom: 40px;
   border-bottom: var(--divider);
+  user-select: none;
   > a
   {
     height: 38px;