A DIV is a block level element just like
A block-level element always starts on a new line and takes up the full width available (stretches out to the left and right as far as it can).
This behaviour can be changed by using style rules (CSS).
Do dives have sizes?
Sure they do. In simplest terms, a division is a box. Refer to the CSS Box Model.
A division's size is its width + margins + padding + borders. Height is determined by content inside the box. Thus there's no need to set explicit height values on divs that contain content.
In responsive layouts, we typically give divisions a % width instead of fixed pixels. But there are times when you might need to use other CSS Units .