Website page scrolling fails with overflow

I can not see the full page  at some of the website 

here is an example :https://www.minecraft.net/zh-hans/get-minecraft

as you can see , if you click the "compare platforms & features" button, you can not see the full content.

you can solve the problem just delete the "overflow" attribute in the class which named "modal-open". 

my english isnot that good. hope you can fully understand what i express above.

thanks.