Button color accessibility

Some buttons have insufficient text contrast. For some reason we have two different button implementations:

1. Enough contrast: Styled automatically via `src/layouts/CTButtons/styles.js`
2. Not enough contrast: Styled manually via `src/components/stylesheets/general.vars.css`

We could fix option 2 in isolation, but ideally we would just unify all buttons to use option 1.

Start by comparing the button styling in src/layouts/CTButtons/styles.js with the manual rules in src/components/stylesheets/general.vars.css. Determine whether the two implementations can share the automatically generated styling without losing existing behavior. Done means all buttons meet text-contrast requirements and no separate manual button styling remains, as appropriate.

Written by the indexing model from the issue text.