This record when a regular flow box floating box encountered a problem:
Floating box arrangement will avoid the conventional flow box.
Conventional box ignores the floating box arrangement.
(They are more on a box attribute to judge.)
This throws up another problem, height collapse.
The height of the collapse is actually normal flow box will ignore when calculating the height of the floating box, so highly collapsed.
Can be used to solve the collapse height: clear: both; float removed.
Reasons for the collapse of highly element is actually not the actual height will collapse.