Define header image in Functions.php or style.css

Hello sir,
I am using dazzling child theme for mobile devices. For desktop I am using a different theme. Now I want to define a different header image through functions.php and style.css or with anyone of them. I cant edit it in my primary theme for dextop, It affects the dextop appearance. So have to make changes to functions.php and style.css of dazzling child theme.

So please guide me to define header image in child theme. I don’t have access to wp dashboard for this theme. Only I can made changes through FTP in Child theme files.

Thanks

This is request for custom development therefor I can’t help you with that.

The basic idea is to use CSS media queries to show different image based on device screen size.

Here are some basic CSS media queries that you can use

@media (min-width:320px) { /* smartphones, portrait iPhone, portrait 480x320 phones (Android) */ }
@media (min-width:480px) { /* smartphones, Android phones, landscape iPhone */ }
@media (min-width:600px) { /* portrait tablets, portrait iPad, e-readers (Nook/Kindle), landscape 800x480 phones (Android) */ }
@media (min-width:801px) { /* tablet, landscape iPad, lo-res laptops ands desktops */ }
@media (min-width:1025px) { /* big landscape tablets, laptops, and desktops */ }
@media (min-width:1281px) { /* hi-res laptops and desktops */ }

These are just general examples and you won’t need all of theme but maybe 2 or 3 of theme but I am just showing how flexible it can be.

Inside those media queries you can add any custom CSS that will be printed only for devices with defined size.
If you are not familiar with CSS you will have to hire someone from Freelancer or Upwork (formed oDesk) to do this task.

Sorry for inconvenience.