Iframe returns a frame smaller than expected

I try to implement an iframe as HTML code directly in the page (not in snippet or template). In principle it works, but the height is always 154px, independent of the height=‘365’ or whatever else I put in.
Here is the code from wetter-online:
<iframe marginheight='0' marginwidth='0' scrolling='no' width='300' height='365' name='FC3' style='border:1px solid;border-radius:10px;border-color:#00537f;' src='https://api.wetteronline.de/wetterwidget?gid=10382&modeid=FC3&seourl=berlin&locationname=Berlin&lang=de'></iframe>

Do I do something wrong?

Best regards

Probably due to some styles or the parent container? This has nothing to do with Kirby, actually.