function.php file issues

Hello,
I’m going crazy here. Using a twenty eleven child theme, I’m attempting to edit the function.php file to add thumbnail image sizes, and when I edit the file and upload it, I get a blank screen. When I upload the original functions.php file I get a blank screen too.
I have been reading codex, support, and third party websites for hours, and I cannot figure out why this is happening.
here is the site: https://www.elainegriffindesigns.com/tester/
Any advice would be so appreciated. Thanks!