SOURCE

var oBox = document.querySelector("#box"),
  oTitle = document.querySelector("#title");
oTitle.addEventListener("mousedown",function(event){
  var moveX = event.offsetX,
    moveY = event.offsetY;
  document.addEventListener("mousemove",fnMove);
  function fnMove(e){
    oBox.style.left = e.clientX-moveX + "px";
    oBox.style.top = e.clientY-moveY + "px";
  }
  document.addEventListener("mouseup",fnUp);
  function fnUp(){	
    document.removeEventListener("mousemove",fnMove);
    document.removeEventListener("mouseup",fnUp);
  }
})

<div id="box">
  <div id="title">消息提醒</div>
  <div id="massage">暂时没有......</div>
</div>

*{margin: 0;padding: 0;}
#box{
  width: 300px;
  position: absolute;
  top: 100px;
  left: 100px;
  -webkit-user-select: none;
}
#title{
  width: 100%;
  height: 50px;
  background: #4169E1;
  color: aliceblue;
  line-height: 50px;
  text-align: center;
  cursor: move;
}
#massage{
  width: 298px;
  height: 200px;
  border: 1px solid #4169E1;
}