Items keep leaving their desired place (Flex-box) : As the title says, the item keeps leaving their place what I've set them to.

The issue results in the website not being responsive, when the screen zooms to 125%
You may see this website for the result - http://joshuacote.xyz/


Do you think, you can help out what's been the issue?

I'm pretty sure its the usage of flex-box, but I've tried most things I could.

This is what issue is being caused - 

https://i.gyazo.com/2db36c2f2c219968b48bc7ddb6c075b2.png