Menu button is hardly visible on mobile phones

[wilzbach]

I really feel bad for being the only one reporting issues, but the menu button is just a grey box:

Here's a CSS quickfix that works for me:

.site-branding .secondary-toggle {
  background-color: grey;
  color: grey;
}
.site-branding .secondary-toggle a.hamburger::after {
    content: "\f0c9";
    font-family: FontAwesome;
    color: white;
    font-size: 30px
    margin-left: -17px;
}