clearfix用のmix-in

@include clearfix;

@mixin clearfix{
  .clearfix:before, .clearfix:after {
    content: "";
    display: table;
  }
  .clearfix:after {clear: both;}
  .clearfix {
      *zoom: 1;
      &:before, &:after {
          display: block;
          height: 0;
          visibility: hidden;
          content: "\0020";
      }
      &:after {
          clear: both;
      }
  }
}