Wootheme Mystile : Open Sans font issue

Hi,
I’m using the Mystile theme for woocommerce on a site I’m building : https://atelierartisti.fr/ . I use the Open Sans fonts in the Mystile options.

I got 2 issues :
– choosing “thin” in the menu selector has no effect. The font is bold. I must redefine the css rule in order to have a 400 normal open sans font.

after redefining the css rule , the man nav is no longer visible with Safari. It’s ok with Light 300 open sans, but no other.

Is this a known bug ?How can I solve this ?

Thanks