Footer hr not adjusting properly to contrast themes

[BlueSlug]

Describe the bug

The background of the horizontal rule in the footer is unset when contrast themes are active, which results in inconsistent behaviour between them and across browsers.

The solution may be to disable the border CSS rules, though exploration and testing is required.

To Reproduce

Steps to reproduce the behavior:

1. Activate one of the affected contrast themes
2. Scroll down to the page footer
3. See error

Expected behavior

The colour of the hr should respond to the contrast theme and not have any gaps within it (i.e. solid rather than an outline)

Screenshots

Chrome default

Chrome bw

Chrome wb

Chrome by

Chrome yb

Chrome ldgd

Chrome gw

Chrome gd

Chrome bbr

Firefox bbr

Desktop:

N/A

Smartphone:

N/A

Additional context

N/A