Unhide the header and footer

Hello, I am not experienced with code. I was trying to see if I could only hide the footer. I read a blog that said to insert a code block and then add a particular css code. 

<style>
.header, #footer-sections {
display:none !important;
}
</style>

I was just going to experiment with it and hit "save" and now the header and footer disappeared. When I click on Edit, the header and footer don't show. So I cannot delete the code block I added. Can someone help me unhide it so I can remove the code and get my site back? 

Suppose your site is venkat.squarespace.com

You can access this link: venkat.squarespace.com/config/safe

This link will disable all custom code in Edit Mode, then you can remove above Code Block.