1. Please send us example link to page where you got such header image first.
2. If you want to set custom page instead of pre-defined "Under Construction", you need to create own page and then set it up under Theme options > Pages > Under Construction section.
Comments
there is no need to modify theme files because you can do this easily under Theme options > Fonts > Size & Style section.
Thanks!
2. If you want to set custom page instead of pre-defined "Under Construction", you need to create own page and then set it up under Theme options > Pages > Under Construction section.