The white-background was introduced to make the paper-buttons within the Manage User web-dialog have white background.

I think this actually contradicts the purpose of the "hairline button", and hinders usages of such button on darker backgrounds in general.

I think we should revert the paper-button's default background to transparent, and just make it white for the manage user dialog, to reduce the chance of an unexpected breakage on dark background somewhere else.

 Issue 856918  has been merged into this issue.

> I think we should revert the paper-button's default background to transparent, and just make it white for the manage user dialog, to reduce the chance of an unexpected breakage on dark background somewhere else.

+1.

For now, I'm going to take the suggestion of not setting the bg-color for the default paper-button since it's a change with a larger potential impact versus changing the user-manager paper-button bg-color to white. For cr-toast, I will still set the bg-color to transparent since it is more explicit this way. Also scottchen@ noticed the bg-color needs to be fixed for the hover state as well.

This is fixed in https://chromium-review.googlesource.com/c/chromium/src/+/1115354

 Issue 857507  has been merged into this issue.