Custom css shows in edit mode but disappears when i save

Site URL: https://amphibian-carrot-kfs3.squarespace.com/boka-tid

When i use my custom css for booking appointments it is only visable while editing. As soon as i click save it disappears for some reason.

<iframe width="100%" height="800" src="http://ww1.clinicbuddy.com/onlinebooking/-74" FRAMEBORDER="no" BORDER="0" SCROLLING="no"></iframe>

Have been using this code from my old website at wordpress where it worked with no problem, can't seem to figure out what the issue is here. 

2 hours ago, simonjansson_ said:

Site URL: https://amphibian-carrot-kfs3.squarespace.com/boka-tid

When i use my custom css for booking appointments it is only visable while editing. As soon as i click save it disappears for some reason.

<iframe width="100%" height="800" src="http://ww1.clinicbuddy.com/onlinebooking/-74" FRAMEBORDER="no" BORDER="0" SCROLLING="no"></iframe>

Have been using this code from my old website at wordpress where it worked with no problem, can't seem to figure out what the issue is here. 

Skärminspelning 2022-05-17 kl. 12.56.59.mov

you can set css by adding code to Home > Design > Custom Css

https://support.squarespace.com/hc/en-us/articles/206545567-Using-the-CSS-Editor