MC-3992: Columns Widths Are Not Consistent Between Stage & Storefront

- Added box-sizing style to column content type

Author: Hwashiang Yu

app/code/Magento/PageBuilder/view/frontend/web/css/source/content-type/column/_default.less

@@ -7,6 +7,10 @@
 //  Default appearance styles
 //  _____________________________________________
 
+.pagebuilder-column {
+    box-sizing: border-box;
+}
+
 @media only screen and (max-width: @screen__m) {
     .pagebuilder-column {
         flex-basis: 100%;