Chore: add theme (#15361)

examples/entry.js

@@ -25,6 +25,19 @@ Vue.component('main-header', MainHeader);
 Vue.component('side-nav', SideNav);
 Vue.component('footer-nav', FooterNav);
 
+const globalEle = new Vue({
+  data: { $isEle: false } // 是否 ele 用户
+});
+
+Vue.mixin({
+  computed: {
+    $isEle: {
+      get: () => (globalEle.$data.$isEle),
+      set: (data) => {globalEle.$data.$isEle = data;}
+    }
+  }
+});
+
 Vue.prototype.$icon = icon; // Icon 列表页用
 
 const router = new VueRouter({