You can write project documentation in plain HTML, and that gets the job done. However, plain HTML styling may feel a little spartan. Instead, try adding a few simple styles to an HTML document to add a little pizzazz to documentation, and make your documents clearer and easier to read.
You can use styles to make your documents easier to read. Seeing you're just starting to learn about styles, just a few simple style elements are covered in this linked article:
* background-color to set the background color
* color to set the text color
* font-family to use a different text font
* margin-top to add space above an element
* margin-bottom to add space below an element
* text-align to change how the text is displayed, such as to the left, to the right, or centered
See Level up your HTML document with CSS
Use CSS to bring style to your HTML project documentation.