Child themes overriding parent styles bug

[Gofish]

In theme preview in the Wordpress admin, Child themes do not show a proper thumbnail.

Also, I have a child theme that uses a style.css that overrides the parent's style.css, and Wordpress says the active theme is broken.

[Gofish]

Broken preview

[demetris]

1. Preview thumbnails are not generated by WordPress. You need to include one in your (child) theme’s folder. If you don’t, you see what you see now.

2. I’m not sure I understand: The parent style.css is overriden by default when you use a child theme. (Its rules are not used at all unless you import it explicitly into the child’s style.css.)

[Gofish]

Thanks...I think it was because I was using switch_theme in the parent theme to switch to the child theme while the child theme was active and it caused a bug.