Color Contrast Failure (Dark Mode) in section C.1 Normative references

[clapierre]

Section

https://w3c.github.io/epub-specs/epub34/annotations/#normative-references

Describe the problem

When you switch the theme from "Light" to "Dark" for the Normative References section.
The color contrast of this section fails WCAG 1.4.3.

Describe the fix or new feature you propose

I think removing the light blue background like is done in Informal References will resolve this issue.

[iherman]

@clapierre you are right but we are not the ones to change that: we are relying on the core W3C style sheets (including for DM).

Copying to @deniak