At the same time, ask yourself "do I really need something special for this?" because the browser adds native support for things all the time.

I find that most datepickers are better than the browser's default. It's a shame that they can't be styled more

Totally agree. What do engineers or designers think they're trying to accomplish when they mess with the scroll bar? Or the password field? "We are so sophisticated, the built in behavior is simply not good enough for us!"

Congratulations, now your website is a shitty experience for your users. Well done.