.container {
  height: 100%;

  .left-side {
    float: left;
    width: 300px;
    height: 100%;
  }
  .contents {
    float: left;
    width: calc(100% - 360px);
    height: 100%;

    .messages {
      width: 100%;
      height: 100%;
    }
  }
  .right-side {
    float: left;
    width: 60px;
    height: 100%;
  }
}