Create a rectangle with only a border that automatically resizes

Hello,

I'm trying to create a rectangle transparent background with only a border that the user could resize in the fluid engine easily (without having to note its size by hand in the code and find the # of the block) 

So far I have done this: 

Custom code HTML :

<div id="square"></div>

CSS :

#square {
    width: 100%;
    height: 100%;
    background-color: transparent;
    border : 2px solid red;
  }

The width follows well (it fills the entire width). But not the height.

Do you have an idea ? A particular class to add to my div maybe?  Or better option ?

Thank you very much! 

Page : https://vanilla-yellow-j6gf.squarespace.com/test

Password: demo 

PS: Sorry for my bad English. It's google translate haha.

Hi,

You try changing that section to Classic Editor section.

I had a similar problem yesterday, then I changed to Classic & it disappeared.

Thank you for the option, but I want my clients can resize it with the fluid engine 😉 I want to use it as a decor/design element 🙂

If so, I have no idea. You try posting to some SS groups on Facebook