Testament System Sans Serif chosen, but serif font displayed

Store Design
1

Hi together,

in the website settings under fonts I changed all three fonts: navigation, body and header to the system sans-serif option, but its displayed the serif option. Any idea how this can happen?

I use the Testament Theme.

2

@huks
Put below code into base.css file
online store->theme >Edit code->Base.css

@font-face {
  font-family: sans-serif;
  src: url(sansation_light.woff);
}

change src url according to your file name .