Please don't quote something you clearly don't understand.
XenForo is actually compliant with the above (outdated) link on almost all of the points.
And none of that document mentions ANYTHING about the non-issue reported in this post.
If you want to talk about accessibility, it is a completely different discussion than what this thread is about. This thread is about using CSS which sits on top of the web content. Which is accessible, clearly.
Blind or bad eye sight, otherwise visually handicapped, or physical handicap requiring a third party machine to translate and use online sites, browsers, etc, will have no problem with the following web content, such as the menu, with and without the design.
Having albinism myself, with glasses on I see about 25% of what a normal person at 80%-100% might see, there's no difference in the clarity of the font itself, the transparency is to the menu, not the font. Which is very easy to read on a system that uses clears the fonts up such as OSX and later versions of Windows - or especially designed for assisted / accessible devices / programs.
Since it is just feedback, thanks for sharing. Solution to your individual problem: Change the CSS again on your own site. On the average XenForo site I can tell you that the majority won't even notice this subtle change. And that those who do notice it find it nice, and will not notice a decrease in readability.
From the millions of visitors to thousands of XenForo sites, I bet you're the only one pulling the accessibility card. Reason: You clearly don't know what you're talking about and it's a pure insult for those who are depending on sites being conform these w3c RECOMMENDATIONS.
Yes; w3c is not mandatory, it's a recommendation. And still, XenForo is checking the checkbox on 9 out of the 10.
Find me 20 fortune 500 web sites that can match XenForo's approach.
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