How to make a round border with a gradient at the link?

Question

css

and while the link (kind of like a button) was transparent, that is, the background under the button was visible.

Answer 1

the question as a whole is not clear at all, answer in parts:
for this there is a css property background: transparent;
What?
for this there is css property border-radius: 20px;
https://css-tricks.com/examples/GradientBorder/