header image not showing in mobile device

Hi

Please add the following CSS code in Appearance -> Customize -> Additional CSS

@media only screen and (max-width:767px){
    .site-header{
        background-size: 100% 100% !important;
        background-position:inherit !important;
    }
}

I hope this will help you.

Kind Regards

Thanks Prashant Singh it worked ,thanks for the quick support.