Thanks for this explanation. Now I have my favourite font family – but on mobile the font size is still small. Do you have how I can change this in custom.css?

@Claudia In general: I would suggest to adjust the “Font Scale” settings in the Theme settings. This would be global, but if your new/custom font looks smaller, than it will be smaller everywhere. 

There is no easy way to just increase the size on mobile. You would of course need to use a media query, but you would also have to specifically target certain CSS classes and there are so many of them. 

Thanks. Even I choose standard font size with "Font Scale", no matter what I do, on mobile the font size is 13px. I'll have to look for a solution at IPS.

1 hour ago, Claudia said:

Thanks. Even I choose standard font size with "Font Scale", no matter what I do, on mobile the font size is 13px. I'll have to look for a solution at IPS.

I had a look at your site. The forum text on mobile should come from this declaration, which you should be able to override in the custom.css

@media screen and (max-width: 767px)
.ipsType_normal {
font-size: 13px;
}
}