Currently, the .user-css class can target three separate sections of HTML. Of these three:

• Only one is easily selectable on its own using only class selectors (.user-css.world-global-header).
• Using only class names, the other two can only reliably be selected with .user-css.page.
• One of these can be selected using an ID selector (#world-navigation-sidebar, but modern CSS linters will warn you against that at best.
• The other technically has a unique class assigned to it (.main-container), but the class name is blocked by the security filters.

  At the moment, the differentiate between the last two, I have to use #world-navigation-sidebar.user-ss and .user-css.page:not(#world-navigation-sidebar), which isn't ideal.   To fix this, I'd recommend adding a new unique class name to both blocks: .user-css-world-navigation for #world-navigation-sidebar, and .user-css-body or .user-css-main for .main-container.