Active State for menus in 1.13.0 with Smoothness Theme
The active state for menu items in the default theme has a blue background and all the other themes I checked makes the active item stand out visuall... but the smoothness theme only adds a light gray border. It's also different from how it looked in 1.12. I'm not sure if this is a bug or intentional. Either way, I think it could be improved.

@mgol I'm wondering why the label "Behavior shared with 1.12" was added. For me it's different in that version as shown in the screenshots.
I have jQuery UI 1.12.1 in the Smoothness theme downloaded locally and it looks just like in 1.13.0, i.e. your second screenshot. Your first screenshot is the Base theme, isn't it?
Can you share screenshots of 1.12.1 & 1.13.0 in the same theme so that I can see what differs for you?
Oh yeah. I was having a hard time finding an example of Smoothness. The thing I was working on would have been quite difficult to revert, so I used the base. But I was able to find an example of what 1.12.1 looked like

I was wondering if maybe the issue lies in the theme builder itself?
This doesn't look like the smoothness theme to me. I still see no difference in what 1.12.1 & 1.13.0 look like, 1.12.1 is also not highlighted other than by adding a gray border. I'll leave the labels for now. If you find a difference, please post here & we can re-evaluate.
Yeah, you might be right. I might have been a modified version of Smoothness because this issue previous existed.