The "refine your search" link on the OPAC search results page (opac-search.pl) is hard to read (grey text on a grey background) and doesn't meet accessibility guidelines.
WCAG 2.1 1.4.3 Contrast (Minimum) Level AA:
"The visual presentation of text and images of text has a contrast ratio of at least 4.5:1, except for the following:
- Large Text: Large-scale text and images of large-scale text have a contrast ratio of at least 3:1;
- Incidental: Text or images of text that are part of an inactive user interface component, that are pure decoration, that are not visible to anyone, or that are part of a picture that contains significant other visual content, have no contrast requirement.
- Logotypes: Text that is part of a logo or brand name has no contrast requirement."
There are several free websites for checking the contrast ratio, e.g. https://webaim.org/resources/contrastchecker/
You can also use the built-in accessibility functions in Firefox and Chrome, as well as specialist accessibility browser extensions like WAVE (https://wave.webaim.org/)