fix sticky demo bug

src/settings.js

@@ -2,6 +2,7 @@ import variables from '@/styles/element-variables.scss'
 
 export default {
   theme: variables.theme,
+
   /**
    * @type {boolean} true | false
    * @description Whether show the settings right-panel

src/views/components-demo/sticky.vue

@@ -1,6 +1,6 @@
 <template>
   <div>
-    <sticky class-name="sub-navbar">
+    <sticky :z-index="10" class-name="sub-navbar">
       <el-dropdown trigger="click">
         <el-button plain>
           Platform<i class="el-icon-caret-bottom el-icon--right" />

src/views/example/components/ArticleDetail.vue

@@ -1,7 +1,7 @@
 <template>
   <div class="createPost-container">
     <el-form ref="postForm" :model="postForm" :rules="rules" class="form-container">
-      <sticky :class-name="'sub-navbar '+postForm.status">
+      <sticky :z-index="10" :class-name="'sub-navbar '+postForm.status">
         <CommentDropdown v-model="postForm.comment_disabled" />
         <PlatformDropdown v-model="postForm.platforms" />
         <SourceUrlDropdown v-model="postForm.source_uri" />