Highlighted tabs on the bottom of the apps

Hello!

I'd like to ask for an advice.

I will describe it on the example of Iphone's App Store, but it occurred in Clock app as well and some other apps. So, when I open the App Store on my Iphone, the tabs on the bottom - "today, games, apps etc" are glowing now. I don't know what happened or what have I done but those buttons are fully highlighted like with square instead of just words " today, games, apps" itself highlighted as was before. How do I turn it back? (The last thing I did was turning on the greyscale in Accessibility but I immediately turned it off so I couldn't mess up the settings)

Sorry for chaotic explanation. But I would appreciate if anyone knows what should I do.

Thank you