code in the block can't remove

I program to use the general version.
And I added a new code in the block, which is a button that I wrote css to make it hover in the bottom right corner.
Now I want to remove it after testing, I can see the button on the page but I can't click to remove it, please guide me!
Thanks for your help!

Thank you for your response. I was able to safely remove/modify the CSS tag as expected. I’d like to ask if it’s possible to embed CSS + HTML and JavaScript syntax directly into the page. I’m trying to control the movement of the "back to top" button.

You can add code to Page Settings > Advanced > Page Header Code Injection for the page. Please see per-page code injection.

Alternately you can use Code blocks in the page itself.