How to create a WordPress theme?

Question

WordPress

Hello! I understand the question is not a lot of volume, but still I will be grateful if you help me figure it out.
I wrote a topic on Wordress for myself, but when I wrote it, I ran into such a problem ...
There are 4 pages, one parent, three child, they are also tied to the corresponding headings. They have the same design except for the color of some elements. The parent page displays its content and at the bottom are the headings and thumbnails of the posts of the child pages. Child ones display their content and at the bottom headings with thumbnails of posts of their category. I solved it this way: I created 4 static pages like page-slug.php. Everything works, but it seems to me that this is not correct.
Question?!
Is it possible to do this somehow using one page template, and so that the content changes dynamically depending on the selected page? Well, if possible, and the color of some elements?

Answer 1

Well, you make one page initially general, and then with the help of if you add classes and other things