As you have seen a div will grow to fit the content. Sometimes though you might want it to be at least a certain size even if that leaves empty space inside.
Save overflow.html as min.html and delete the overflow and height lines in the style sheet. Try the page and you should see that the div has grown to fit the content as before. Now delete all the paragraphs apart from one. Save and view. The box shrank as you probably expected.
Now add this line to the styles:
Save and view. Copy more paragraphs back in - keep going until they do not fit in the minimum height. The div should grow unlike when you used height.
You can set a minimum width in the same way. Both mean div elements will be at least a certain size but they can still grow if needed.