In STUDIO, "Group Selection" function allow you to add a parent box as a single top level layer to combine elements together. The parent box added by this function will be named <div><group> and you can edit it just like a normal box.

Select the boxes that you want to group.

You can use the right-click menu item "Group Selection" or the shortcut key ⌘ + G to group the selected elements.

Also, if you want to ungroup/delete only the parent box while leaving the child boxes, press ⌘ + Shift + G with the parent box selected.