Header colour

Small question – I can’t seem to change the HOVER colour of the heading. It’s red. I’ve tried changing it using a custom CSS plugin, a child theme, and I’ve even tried changing it in the original CSS – nothing works. So I assume I’m changing the wrong thing.

I assumed I needed to change

.site-title a:hover {
color: # (my chosen HEX value) ;
}

but that doesn’t work, so can someone tell me where it is?