设置了绝对定位让 div 在页面水平垂直居中，完了在设置了拖拽之后出了问题，拖拽的时候会飘，去掉 top: 0;left: 0;right: 0;bottom: 0;的时候就可以正常拖拽了，这种情况该怎么办啊

        #login{             width: 500px;             height: 300px;             text-align: center;             border: blueviolet 1px solid;             position: absolute;             margin: auto;             top: 0;             left: 0;             right: 0;             bottom: 0;             display: none;         } 

 var login = document.getElementById('login')                  login.onmousedown = function(e){             var l = e.clientX - login.offsetLeft             var t = e.clientY - login.offsetTop              document.documentElement.onmousemove = function(e){                 var x = e.clientX - l;                 var y = e.clientY - t                 if(x <= 0){                     x = 0                 }                 if(y<=0){                     y = 0                 }                 if(x >= document.documentElement.clientWidth - login.clientWidth){                     x = document.documentElement.clientWidth - login.clientWidth                 }                 if(y >= document.documentElement.clientHeight - login.clientHeight){                     y = document.documentElement.clientHeight - login.clientHeight                 }                 login.style.left = x + 'px'                 login.style.top = y + 'px'             }             document.documentElement.onmouseup = function(e){                 document.documentElement.onmousemove = null             }         }   

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