文档细节优化，search、咯阿丁和dialog组件样式修复 (#5)

* fix: loading small style, search style and dialog style

* fix: scroll to top

* fix mobile scroll

* fix scroll to top

packages/vant-css/src/actionsheet.css

@@ -21,16 +21,13 @@
 
     @e item {
       line-height: 50px;
+      height: 50px;
       text-align: center;
       color: $c-black;
       font-size: 16px;
       position: relative;
       background-color: $c-white;
 
-      @m loading {
-        padding: 10px 0;
-      }
-
       &::after {
         @mixin border-retina (top);
       }
@@ -43,6 +40,7 @@
 
     @e loading {
       margin: 0 auto;
+      display: inline-block;
     }
 
     @e button {