Your main navigation is long enough that it doesn’t fit in the available space and overflows onto the header image.
To avoid this you can either rearrange your menu items so they take up less horizontal space or force-activate the mobile menu earlier:
@media (max-width: 123px) {
.cryout #nav-toggle {
display: block;
}
.cryout #branding {
margin-right: 3em;
}
#masthead.cryout #access {
display: none;
}
}
Replace 123px
with the screen width value when the menu starts overflowing (or a few pixels before).