How to style the underline of the hyperlink-text?

I have hyperlinked my text (paragraph) and would like the line of the link to not thicken on hover. I want it to stay like in the first image. Which code can I use for this?

I am using this template: https://meriden-demo.squarespace.com/
And I uploaded custom fonts via the CSS Box.

Thank you so much!

Are you using a template? If so, let us know which one.

If not, you need to remove the code that is thickening the link on hover rather than adding code to not do that.

@qosmic Yes, sorry: It is this one: https://meriden-demo.squarespace.com/
And I uploaded custom fonts via the CSS Box.

Add to Design > Custom CSS

a:hover, a:hover span {
    background-size: 100% 1px !important;
}