Donate block: highlight not working

Hello,

In my donation page I'm using the Jetpack donation block. Unfortunately, when a user clicks on the chosen amount, nothing happens, i.e. the highlight doesn't work. Instead, it works when a user chooses one off, monthly or yearly donation.

I've asked wordpress.com: they say I have to ask the theme developer. They suggested the following customized CSS code but there's no use:

/* Better highlighting for the donation block UI | 4765211-zen mh */
.donations__amount.is-selected, .wp-block-jetpack-donations div.donations__nav-item.is-active {
  background: #32373c;
  color: white;
}

Any suggestions?

Thanks,

Mario