Bug 29068: Accessibility OPAC search results summary text has insufficient contrast

Bug 29068: Accessibility OPAC search results summary text has insufficient contrast

This patch changes the colour of the label text in
OPAC search results to increase the contrast ratio,
improve accessibility and make the text easier to read.

To test:

1. Search for something on the OPAC
2. Use an accessibility tool (e.g. Chrome's Lighthouse
   tool) to check the contrast ratio
3. Confirm that the labels (Edition, Format etc.) in the
   results summary have insufficient contrast
4. Apply the patch and rebuild CSS:
   yarn build --view opac
5. Use the accessibility tool to confirm the contrast
   ratio now meets minimum accessibility requirements
6. Check that the OPAC still looks ok after the changes

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>