改變<br>的高度

http://stackoverflow.com/questions/1409649/how-to-change-height-of-a-br

br:nth-of-type(n+4) {
   display: block;
   margin-top: 0;

   line-height: 0;
}

chrome瀏覽器要加：

content: " ";

讓第四個以後的br高度消失
IE7, IE8要在jquery多加jquery-extra-selectors.js