[Task]: Improve accessibility of website

### What needs to happen?

Improve the accessibility of our website.
It seems our website is not compliant on some aspects.
https://lists.apache.org/thread/c9mw7319jjoq4yj50k1o7zon6rwwntn7

### Issue Priority

Priority: 3

### Issue Component

Component: Website

Start with the linked Apache mailing-list discussion to identify the accessibility aspects that need attention, then locate the website sources it references. The issue names no files, tests, or specific compliance failures, so done should be defined from the agreed accessibility requirements before implementation.

Written by the indexing model from the issue text.