The fix height of the CSS is missing

This method is Baidu Encyclopedia mobile phone page with, first for fixed positioning elements set a parent element, no height, no width, nothing, his first child element is we need to do fixed positioning elements, this according to the needs of writing a good style, at this time, the height of the parent element is still 0, how to make the parent element has height, The parent element has a height, the next module does not have to set the value of the margin-top, we just write a fixed positioning element behind an equal height of the empty div is resolved, then the parent element has a height, and it is the height we need, this empty div like a pillar, supporting the castle in the air.

The fix height of the CSS is missing