overflow

The overflow CSS property specifies whether to clip content, render scroll bars or display overflow content of a block-level element.
 
Using the overflow property with a value different than visible, its default, will create a new block formatting context. This is technically necessary as if a float would intersect with the scrolling element it would force to rewrap the content of the scrollable element around intruding floats. The rewrap would happen after each scroll step and would be lead to a far too slow scrolling experience. Note that, by programmatically setting scrollTop to the relevant HTML element, even when overflow has the hidden value an element may need to scroll.

<!DOCTYPE html>
<html>
    <head>
        <style>
            p {
                width: 12em;
                border: dotted;
                overflow: scroll; /* append scrollbars if necessary */
				height:80px;
            }
        </style>
    </head>
    <body>
        <p>
            <b>Note:</b>
            The quick brown red fox jumps over the lazy dog
            The quick brown red fox jumps over the lazy dog
            The quick brown red fox jumps over the lazy dog
            The quick brown red fox jumps over the lazy dog
            The quick brown red fox jumps over the lazy dog
            The quick brown red fox jumps over the lazy dog
        </p>
    </body>
</html>