Ok I can access your site.
I was hoping I could narrow down the issue by looking at your Child Theme style.css file but there is just too much code there.
Is that all your custom code? If not then you shouldn’t have copied the Mantra theme’s style.css code like that, you need to use the “@import” line as exampled by Codex: https://codex.www.ads-software.com/Child_Themes#How_to_Create_a_Child_Theme
So you should remove the code that you’ve copied over and instead the top of your Child Theme style.css file should be:
/*
Theme Name: Mantra child
Template: mantra
*/
@import url("../mantra/style.css");
/* =Theme customization starts here
-------------------------------------------------------------- */
