Zero opacity turns to 30%

Thank you for a very useful plugin! However, I noticed a small bug and found a solution as well.

What I need is autohide and transparency. But if I set Admin bar opacity (inactive) to 0%, the bar is not invisible in the front-end. When I go back to settings, I can see that the Admin bar opacity became 30% itself.

Then if I set opacity to 0.01% or 0.25%, somehow it becomes 0% later and the bar is transparent and works well.

But if I decide to save the settings again, when the opacity is 0%, it turns back to 30% again as soon as I go to the front-end.

WP 5.7, PHP 7.2.34