Hello,

Please add this code to the Theme Settings > Custom CSS > Global:

body .mobile-nav .icon-sub-menu:after,
body .mobile-nav .icon-sub-menu:before {
    background-color: #000000;
}
body .mobile-nav ul li .up-icon{
background:#ffffff;
}
body .mobile-nav .searchform input[type=text] {
    color: #000000;
}
body .mobile-nav {
    background-color: #ffffff;
}
body .mobile-nav .searchform button {
    color: #000000;
}

Best Regards