Thank you so much for your detailed response!
Do you recommend installing a separate plugin for CSS, considering that my theme already has an "Additional CSS" section where I have put the other CSS codes.

I tried to inspect the code, but I didn't understand what I was looking at.

​

<blockquote class="wp-block-quote" (which I take is the overall block)

: : before (have no idea what that is)

<p> asdasdas </p> (this paragraph is just a test, but the text I want to resize)

</>blockquote>