Slider shows white background on paper theme with Firefox

[carkod]

Describe the bug

Slider shows white background only with Firefox.

This seems a weird one, looks like a discrepancy in web standard. I couldn't fix it without breaking the other.

To Reproduce

Steps to reproduce the behavior:

1. Here is a codepen with paper background https://codepen.io/carkod/full/rNbePQp
2. Open it with Firefox, you'll see white background, however if you open it with Chrome it doesn't.

Expected behavior

Not sure what is the right thing to do here.

• Override Firefox or override Chrome?
• Target using CSS for a specific browser?

In any case they both should probably look the same.

Quick dirty fix

Screenshots

If applicable, add screenshots to help explain your problem.

Desktop (please complete the following information):

• Browser: Firefox, I'm using 123.0.1 (64-bit), but I bet it happens to any version