FAQ: Sizing Elements - Scaling Background Images

Hello All,

So I have a question relation to scaling background images. I learnt that it is best practice to put all content like images and text in to a html file as html is the structure of a webpage and then the page is styled with a linked css. If an image is added/linked in a html file then how is it styled/ scaled in css? As it would require the image to be removed from the html and then added/ linked in the css with background-image: url();

I am just wanting to know what is the best practice in this case, add/ link images in the css or html?

I have also asked this question in a recent project challenge here