Improve styling of AZ Finder exposed form, especially for multiple vocabulary filters

[bberndt-uaz]

Problem/Motivation

The exposed form for the current Quickstart Finder exhibits a couple styling issues that should be addressed:

1. The spacing between each fieldset element of the form can be inconsistent, especially with filters for multiple taxonomy vocabularies.
2. Top-level vocabulary terms have the same font size and color as the labels for each vocabulary filter, making it difficult to distinguish between the two.

These issues were noticed with an upcoming custom module that uses the Quickstart Finder:

To Reproduce

Steps to reproduce the behavior:

1. Create a page using the Quickstart Finder that uses filters for multiple taxonomy vocabularies (such as the People Finder in the demo content.
2. Observe issues with spacing between the vocabulary filters and text styling of filter labels and top-level vocabulary terms.

Proposed resolution

Update the styling of the Quickstart Finder exposed form to resolve these issues.