样式为float时，上级div的外框不会自动扩大
this is a test for me
this is a test for me
this is a test for me
外框不自动扩大，下一级的标答连续排列
样式为float时，上级div的外框不会自动扩大,如果加上float和height:auto能自动调节高度
float to right
float to right
float to right
float to right
float to left
float to left
float to left
浮动标签，要自动适应高度，在最后加clear:both
this is a test for float
this is a test for float
this is a test for float
this is a test for float
this is a test for float
this is a test for float
this is a test for float
this is a test for float
this is a test for float
this is a test for float
this is a test for float
this is a test for float
this is a test for float
this is a test for float
this is a test for float
this is a test for float
this is a test for float
this is a test for float
this is a test for float
this is a test for float
this is a test for float
