btpxpress-frontend/public/theme/extensions/_megamenu.scss

.p-megamenu {
    .p-menuitem {
        &.p-highlight {
            &.p-focus {
                > .p-menuitem-content {
                    background: $emphasis-lower;
                }
            }
        }

        &:not(.p-highlight):not(.p-disabled) {
            &.p-focus {
                > .p-menuitem-content {
                    background: $emphasis-lower;
                }
            }
        }
    }
}