Bug 29065: Accessibility OPAC clear search history link has insufficient contrast

Bug 29065: Accessibility OPAC clear search history link has insufficient contrast

This patch changes the colour of the clear search history link
on the OPAC to increase the contrast ratio, improve accessibility
and makes the text easier to read.

To test:

1. Go to the OPAC homepage
2. Use an accessibility tool (e.g Chrome's
   Lighthouse tool) to check the contrast ratio
3. Confirm that the clear search history link
   has insufficient contrast
4. Apply the patch and rebuild css:
   yarn build --view opac
5. Confirm that the contrast ratio now
   meets minimum accessibility requirements
6. Check the OPAC still looks ok after the changes

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>