Formatting refences to being bold

I use the Reference style plugin and the Dev theme and I can’t make the references I have put in the Reference style plugin bold. Block references that I haven’t put in the plugin gets bold from my custom.css:

/Customize page link/
:is(, a.block-ref) {
font-weight: bold;

I have tried to look at the css of the plugin but I think my skills comes to a short.