Fonts and size

[kysil]

How to change Font and size in Header (Site name)?

[opentype]

In general:

get a web inspector tool for your browser (e.g. Firebug for Firefox). Use it to find the correct declaration which sets the value you are interested in by clicking on the item. 

Then in 4.0 adminCP go to your theme settings and use the custom.css file to overwrite the default value with your value. For example:

#elSiteTitle {
 font-size:20px,
}