can i copy all the setting (colors, width, etc) from one form to another?

like building a thema and put that theme on all forms

Yes you can, the best thing to do is cloning your form theme each time you want to create a new form, in that way you work the cloned version removing and adding fields, labels, headings, widgets etc.

Here is a guide on how to clone an existing form from your account: https://www.jotform.com/help/27-How-to-clone-an-existing-form-from-your-account

If you need anything else, please open a new thread, we will be glad to assist you.

Also, if you already have an existing form, you can copy the CSS of the form theme, and paste it in the form you want to get same style: