CSS and HTML

Use px for fixed-size elements and precise control. Use % for relative sizing within parent containers in responsive layouts. Use vh and vw for elements that should scale with the viewport size in responsive designs.

Congratulation Steven for completing the project and I hope you had fun building it. Regarding you question on which unit to use I recommend the using rem or em which is explained in the code samples below:

<div>
  <h1>Some text</h1>
</div>

h1 {
  padding: 1em;  //  which is equal to 16px and it is relative to its parent div.
}

h1 {
  padding: 1rem; // this is relative to the root element which is the html tag.
}

So I recommend using em for paddings and margins and rem for font-sizes. Also this link will provide you with a brief overview on them.