feat: 新增 transition 组件

src/component/dropdown/index.less

@@ -14,11 +14,11 @@
   min-width: 100%;
   background-color: #fff;
   box-sizing: border-box;
+  border: 1px solid #e4e7ed;
+  box-shadow: 0 2px 12px 0 rgba(0, 0, 0, .1);
 }
 
 .layui-dropdown dl > .layui-dropdown-menu {
-  border: 1px solid #e4e7ed;
-  box-shadow: 0 2px 12px 0 rgba(0, 0, 0, .1);
   border-radius: @global-border-radius;
 }
 

src/component/dropdown/index.vue

@@ -48,7 +48,7 @@ defineExpose({ open, hide, toggle });
     class="layui-dropdown"
     @mouseenter="trigger === 'hover' && open()"
     @mouseleave="trigger === 'hover' && hide()"
-    :class="{'layui-dropdown-up' : openState}"
+    :class="{ 'layui-dropdown-up': openState }"
   >
     <div @click="trigger === 'click' && toggle()">
       <slot></slot>