The float CSS property specifies that (1) an element should be taken from the normal flow and (2) placed along the left or right side of its container, where text and inline elements will wrap around it.
(1): ?
因为设置了ul li {float:left},这是所有的li其实已经从ul中脱离出来,这里解释为ul感知不到li的存在。而且没有设置ul的height属性,所以ul.height的属性值为0;
(2):为什么ul移动时,li也会跟着移动 ?
虽然ul感知不到li的存在,但是li placed along the left and right side of its container,所以当ul移动时,li也会跟着移动;