Wrong font when displaying website

Hello, i have a Raspberry running Screenly OSE (free).
We use this to display a website, in the websites CSS file it´s configured to display the “Helvetica” font.
However when we display the website it displays it with another font.

Is there any way to change this?
I tried to create a font folder under /etc/pi/.fonts and manually import it into the and do a restart but that unfortunetly didn´t work.