I really dont thing you should use an embed for your form in Hubspot. I've experienced issues with forms not updating through the embed, but also you lose page editor functionality. You should really use a form module I think.
This may be the same with form embeds but I can't say off of the top of my head that this is correct.
I like to give a group or module wrapper to my forms a specific class, like 'form_wrap', then target the form fields beginning with that class. It is a good idea to be specific and deep with your targeting because, in my experience, Hubspot's framework is specific, deep, and takes precedence in the document hierarchy.
Alright, that works nice. But there is one problem. I am editing existing form in hubspot and the feilds like input feild has rounded corners and the submit button too has rounded corner, I just want to make them rectangle. Tried removing all the border-radius from the form CSSbut nothing is changing