CSS styling for filter hover

Hi, hope I can get some help with styling the filter function on our page:

1. How can I have the custom icon show, when the dropdown is open? I added it, when hovering the icon itself, but it does not show when the dropdown is open.

2. I have added a background colour on hover on the dropdown item. How can I style it, so the whole width has a background colour on hover?

3. How can I style the dropdown items, so that they all have a border bottom full width?

4. Last issue, when the dropdown opens, it overlaps with the main filter instead of opening below the filter, how can i move the whole dropdown down, so it is flush with the main filter?

Thanks for your help

The page I need help with: [log in to see the link]