What i've done:
1. Create dir: /wp-content/themes/rt_supra/custom/css-compiled/scss
2. Put in file: custom.scss
3. Add css to file:
#rt-header {
background: url('https://domain/wp-content/uploads/2018/06/wallpaper-e1529327212932.png');
}
It wont work...
If I put background: url('https://domain/wp-content/uploads/2018/06/wallpaper-e1529327212932.png'); in the browser inspector the bg-image is displayed.