fix: hdrReplyListButton double border separator

[frabera]

Fix for the borders of hdrReplyListButton. Before, there was a double border, making the separator bigger. Reply to all button was not affected.

[Deathbyteacup]

Just curious which OS and version of Thunderbird you are using?

I can't see any actual difference in any of these pull requests, so I am just curious if they are OS specific. I don't see anything wrong with them, but they don't seem to be actually making any visual difference.

[frabera]

I'm using Thunderbird 151 on Windows, dark mode. I can provide some screenshots.

It is a minor change, more visible with additional customizations, but there is a double separator and the button background miss the rounded corners.

The infobar animation is more relevant. The wrong css properties break the animation when closing the bar and the empty space is not reclaimed for the mail browser, as in the vanilla Thunderbird. Currently, a dark gray empty space stays where the infobar was located:

Before:

After (also, no animation is shown):