Hamburger menu not visible on NES.css adapter

The hamburger menu icon disappears completely when using the NES.css adapter on mobile. The three horizontal lines are there in the DOM but they are invisible against the dark background.

Steps to reproduce:
1. Switch to NES.css adapter
2. Resize browser below 1024px
3. Hamburger icon is gone

Expected: White hamburger lines on dark background.
Actual: Nothing visible. Menu is inaccessible on mobile.

Browser: Firefox 149, Chrome 135
Device: Desktop (responsive mode) and actual Android phone

Confirmed. The issue is in the NES.css adapter — it doesn't set a background color on the hamburger spans. The base.css hamburger uses \ for the span background, but on NES.css the text color is light on dark and the spans are positioned over the header which is also dark.

Quick fix:
This should go in the NES adapter CSS.

That fixed it. Thanks Consuella. Should we also check Halfmoon? It has the same dark background issue.