Stylus is a Chrome extension which allows you to modify CSS properties.
It's a fork from Stylish without the analytics.
More about it here.
You may wondering, "Why would you want to do that?"
Here's an example of what I did to Youtube's playlist.
See the obvious video length there?
That's my custom CSS.
Not the prettiest, but it makes the video length more obvious to me.
Here's the original for comparison:
So far, I only use it to highlight some content that matters, but isn't too obvious in the original's CSS.
For example, it might be hard to find the delete item button from a shopping cart, or the cancel button from the checkout page.
There's a library of styles created by the community too.
For instance, you might like dark mode for reddit.
Might be able to find some interesting styles there.