Some elements keep main theme CSS values

Step to reproduce:

• Create a new theme "foo" copied from Iceberg
• Change @link-color and @navbar-default-bg values
• Notice that the link color "More applications" and notification icon's background are not updated in the preview, and need a refresh on other pages. It's annoying but actually not the main bug
• Use this theme "foo" on a page "test" on the wiki (and not globally)
• Notice that link "More applications" and notification icon's background keep the values of the global default theme.
• Create a new "bar" theme, and apply it globally. On the subpage "test", these two elements will use the values of the "bar" theme, still not the ones indicated in the "foo" theme.