Improve placement of description for field descriptions

Fields in settings screens have a description, which has been assigned 20px top margin.

This visually groups the description of each field with the next field. Eg in first of attached screengrabs, note that the description "Username to use ..." and label "Password" are placed equidistant to the password field, causing confusion when editing settings.

Trivial CSS fix is to remove the 20px margin top.