Update index.less (#3055)

处理 移动滚动条的时候，ant-select-dropdown 没有随form-item移动

src/design/index.less

@@ -25,6 +25,7 @@ body {
   height: 100%;
   overflow: visible;
   overflow-x: hidden;
+  position: relative;
 
   &.color-weak {
     filter: invert(80%);