• The issue is present in the latest release.
• I have searched the issues of this repository and believe that this is not a duplicate.

Current Behavior 😯

In dark mode, snackbar have a white background and a dark color. However, snackbar actions seems to have the same style as if they were not part of a snackbar. This means that disabled actions appears white on a white background.

Expected Behavior 🤔

Disabled snackbar actions should be visible on dark mode.

Steps to Reproduce 🕹

https://codesandbox.io/s/material-ui-issue-forked-9zlxc

Steps:

1. Configure a custom theme with dark mode enabled
2. Display a Snackbar with a disabled action