I want to add a class (underline) to each element with rel_row_0 class.
I have this code:
<a onclick="document.getElementsByClassName('rel_row_0').classList.add('underline');">X</a>
I having this error message: Uncaught TypeError: Cannot read properties of undefined (reading 'add') at HTMLAnchorElement.onclick
Usually I don't use javascript so i'm not that good at it.
Thanks for all the help!