Remove wildcard selector from meta-box box-sizing.

The child elements now inherit the container’s box-sizing rules.

edit-post/components/meta-boxes/meta-boxes-area/style.scss

@@ -9,7 +9,8 @@
 	 * other elements (such as .button) are unaffected by Gutenberg's style
 	 * because of their higher specificity.
 	 */
-	* {
+	&__container,
+	.inside {
 		box-sizing: content-box;
 	}