Changing menu font weight not showing

I am trying to change the menu font-weight, either via the Jetpack Stylesheet Editor or the WordPress editor in the style.css. But the changes do not appear on my website (https://www.bonneviesvendsen.no)

I have tried:

(in the Jetpack Stylesheet Editor)
#access a {
color: #eee;
display: block;
line-height: 3.333em;
padding: 0 1.2125em;
text-decoration: none;
font-weight: 100;
}

Result: no changes at all. (menu still bold, I want it thin)

If I mark the menu and right click -> Inspect Element, and then change the following:

#access .current-menu-item > a,
#access .current-menu-ancestor > a,
#access .current_page_item > a,
#access .current_page_ancestor > a {
font-weight: thin;
}

The preview displays the menu in thin, like I want. However, when I apply the same changes to either style.css or in the Jetpack Stylesheet Editor, nothing happens when I refresh the page.

Any help would be greatly appreciated.