Add Margin Between Dropdown and Cite Button on Small Screens

[faokryn]

Currently, on small screen sizes the layout of the web app front end changes to place the citation style selection dropdown directly above the Cite button, rather than adjacent to it, to better accommodate the small screen size. However, there is currently no spacing between these two elements in this situation, which is not visually pleasing.

Add a margin between these two elements when they are vertically aligned.