improve the accessibility of the website

[robertoostenveld]

The feedback on neurostars included multiple people suggesting to move away from thewhite-on-black, and @emdupre specifically mentioned accessibility at https://neurostars.org/t/request-for-feedback-reorganizing-bids-website/5476/3

For me personally a11y was a new term, but I figured it out by now.

[Remi-Gau]

I think this is still valid but needs to be made more specific to be actionable