MC-3573: Tabs implementation

- Added tab support

Author: nathanjosiah

app/code/Magento/PageBuilder/view/adminhtml/web/css/source/content-type/tabs/_default.less

@@ -3,6 +3,8 @@
 //  * See COPYING.txt for license details.
 //  */
 
+@color-gray: #ccc;
+
 //
 //  Default appearance styles
 //  _____________________________________________
@@ -173,6 +175,19 @@ div[data-role='tabs'],
         }
     }
 }
+div[data-role='tabs'] {
+    .tabs-navigation {
+        border: none;
+
+        .tab-header:not(:first-child) {
+            margin-left: -1px !important;
+        }
+    }
+    .tabs-content {
+        border: 1px solid @color-gray;
+        border-top: none;
+    }
+}
 
 .pagebuilder-content-type-wrapper.ui-tabs-panel {
     margin-top: 0;