flex常用兼容写法

一般放在common.css中：

.flex{
  display: -webkit-box;
  display: -webkit-flex;
  display: -moz-box;
  display: -ms-flexbox;
  display: flex;
}
.flex1{
  -prefix-box-flex:;
  -webkit-box-flex:;
  -webkit-flex:;
  -moz-box-flex:;
  -ms-flex:;
  flex:;
}
.flex-c{
  -webkit-box-direction: normal;
  -webkit-box-orient: vertical;
  -moz-flex-direction: column;
  -webkit-flex-direction: column;
  flex-direction: column;
}
.flex-a-c{
  -webkit-flex-flow: row wrap;
  -ms-flex-flow: row wrap;
  flex-flow: row wrap;
  -webkit-align-content: flex-start;
  -ms-flex-line-pack: start;
  align-content: center;
}
.flex-j-c{
  -webkit-box-pack: center;
  -moz-justify-content: center;
  -webkit-justify-content: center;
  justify-content: center;
}
.flex-a-i{
  -webkit-box-align: center;
  -moz-align-items: center;
  -webkit-align-items: center;
  align-items: center;
}