Styling and behavior of dialog windows

Before starting this topic, I want to point out that: I am not a programmer, developer or
something like. However, as a user of Photoshop as my main tool for
working since 2006, I decided to try to create my own tool to speed up my flow
of work; JavaScript, css and html, I just started studying in the last few months.

Now my question: I created a and put some function buttons, but I wanted to
that while a was , it could have access to manipulate the image.
Well, I even managed it, but the problem is that I can’t style it without {showModal()}.
I wanted to know if there are possibilities for that.