Current Post/Page Ancestor, CSS

This should be on stackoverflow.

If I understand correctly what you want, you need to change:

.sf-menu li:hover, .sf-menu li.sfHover,
.sf-menu li a:focus, .sf-menu li a:hover, .sf-menu li a:active {
    outline:        0;
    background: #AF1D21
}

with:

.sf-menu > li:hover, .sf-menu > li.sfHover,
.sf-menu > li a:focus, .sf-menu > li a:hover, .sf-menu > li a:active {
    outline:        0;
    background: #AF1D21
}