customize color in WP child theme doesn’t saved

I have a WP theme and I create for it a child version, child version has only style.css file. It loading fine, working normally like mother’s theme. When I use Customize theme function to change color, font-size etc, saved but it doesnt work. Color doesnt load. It works only if I change back to mother’s theme.

So what is the reason? What I missing on child theme?

Thank you