Besides the default logo uploader feature, Sunshine theme has the “mobile logo” uploader feature. Logo uploaded via this feature will only display to mobile visitors of your website.
Upload different mobile logo
1. In WordPress Dashboard, go to Appearance > Customize option.
2. Click to expand the Header Image section.
3. Upload an image logo using “Upload Alternate Mobile Logo” section at bottom.
Use case? If you are displaying a big horizontal banner type logo image, that will look really small on mobile devices (specially height-wise). Hence, using this feature you can display more squarish logo image for better visibility.