What is JotForm?
JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
At JotForm, we want to make sure that you’re getting the online form builder help that you need. Our friendly customer support team is available 24/7.
We believe that if one user has a question, there could be more users who may have the same question. This is why many of our support forum threads are public and available to be searched and viewed. If you’d like help immediately, feel free to search for a similar question, or submit your question or concern.
Yes that's possible when you inject custom CSS codes to your form. Guide: https://www.jotform.com/help/117-How-to-Inject-Custom-CSS-Codes-to-your-Form
If you mean to enlarge the checkbox on the matrix field, you can try the following but this may not work on older browsers. This should work fine on Chrome and Firefox.
However, you can load your form on the Form Designer if you want to customize further your check box field. There's a separate option for the check boxes when you click it on the Form Designer. See these screenshots.
Then use big button size
Let us know if you need further help.
On behalf of my colleague, you are most welcome. We are happy that you got your desired result. We are always happy to assist.
As your additional question is different from the original question, I have moved it to a new thread: http://www.jotform.com/answers/489751
It will be addressed there.