两栏自适应布局，右侧div宽高不定

.main,.sitebar{

      height: 300px;

      font: bolder 20px/300px "微软雅黑";

      color: black;

      text-align: center;

}

.main{

      width: 100%;

      float: left;

}

.main .content{

      margin-left: 200px;

      background: red;

}

.sitebar{

      width: 200px;

      float: left;

      margin-left: -100%;

      background: green;

}

<div class="main">

      <div class="content">hhhhhhhhhhhhh</div>

</div>

<div class="sitebar">

      hehhehhe

</div>