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/search.css

@@ -28,6 +28,7 @@
       color: $c-gray-dark;
       border: none;
       outline: none;
+      -webkit-tap-highlight-color: rgba(0, 0, 0, 0);
     }
 
     @e cancel {
@@ -51,10 +52,11 @@
 
     .van-icon-clear {
       font-size: 14px;
-      line-height: 1;
+      line-height: 16px;
       position: absolute;
       right: 5px;
-      top: 9px;
+      top: 50%;
+      transform: translateY(-50%);
       color: #888;
     }
   }