This is an issue in the Echo extension relating to a recent Codex update. Looks like this relates to Codex which provides background-color and mix-blend-mode.

It seems like when Echo enhances these buttons to be OOUI it should also drop cdx-button cdx-button--weight-quiet cdx-button--icon-only cdx-button--fake-button cdx-button--fake-button--enabled

In T388734#10636989, @Jdlrobson-WMF wrote:

This is an issue in the Echo extension relating to a recent Codex update. Looks like this relates to Codex which provides background-color and mix-blend-mode.

It seems like when Echo enhances these buttons to be OOUI it should also drop cdx-button cdx-button--weight-quiet cdx-button--icon-only cdx-button--fake-button cdx-button--fake-button--enabled

It looks like just removing those classes in my browser console doesn't quite fix the issue:

Also removing .vector-icon helps, but then the hover state is gone:

Also, to clarify, @Jdlrobson-WMF, you're suggesting the fix should be entirely within Echo? If this was caused by a change in Codex, I'd be worried about other places this might have affected.

The longstanding issue here is: T343838: Echo should progressively enhance existing notification icon rather than creating its own - basically Echo has code which swaps out the Codex button for an OOUI button 😭. It then has a bunch of CSS in place that makes the OOUI button look like a Codex. button. Clearly having a button that mixes OOUI and Codex classes is not supported so I don't think this would be impacting other places.

Strategically T142981: Provide a single entry point for notification that anticipates the urgency of the notifications received is where we want to get to on the long run.

In T388734#10637274, @Jdlrobson-WMF wrote:

The longstanding issue here is: T343838: Echo should progressively enhance existing notification icon rather than creating its own - basically Echo has code which swaps out the Codex button for an OOUI button 😭. It then has a bunch of CSS in place that makes the OOUI button look like a Codex. button. Clearly having a button that mixes OOUI and Codex classes is not supported so I don't think this would be impacting other places.

Strategically T142981: Provide a single entry point for notification that anticipates the urgency of the notifications received is where we want to get to on the long run.

I see...I guess I'll move this to following then.