How to style only one image title on image gallery?

Site URL: https://myyvatnettisivut.squarespace.com/

Hi!

How can I apply the desired underline only to one of the gallery image titles shown in the picture.

I want to underline only the third title on the right. But so far I have only been able to underline everytitle or none.

How could I target just one of the titles for a style.

Any advice much appreciated 🙏

Abe

Add to Design > Custom CSS

article:nth-child(3) h2.Index-gallery-item-content-heading {
    text-decoration: underline;
}