在我将 doctype 更改为 html5 后，背景渐变变得混乱，看起来像这样：
如果我再次删除它，它会再次变为平滑渐变。
我的 CSS 代码如下：
body {
background: #3c99d4;
background: -moz-radial-gradient(center, ellipse cover, #81e8f9 0%, #0358b5 100%);
background: -webkit-gradient(radial, center center, 0px, center center, 100%, color-stop(0%,#81e8f9), color-stop(100%,#0358b5));
background: -webkit-radial-gradient(center, ellipse cover, #81e8f9 0%,#0358b5 100%);
background: -o-radial-gradient(center, ellipse cover, #81e8f9 0%,#0358b5 100%);
background: -ms-radial-gradient(center, ellipse cover, #81e8f9 0%,#0358b5 100%);
background: radial-gradient(ellipse at center, #81e8f9 0%,#0358b5 100%);
filter: progid:DXImageTransform.Microsoft.gradient( startColorstr='#81e8f9', endColorstr='#0358b5',GradientType=1 );}