docs(Overlay): add embedded content demo (#4982)

src/overlay/demo/index.vue

@@ -10,6 +10,21 @@
 
       <van-overlay :show="show" @click="show = false" />
     </demo-block>
+
+    <demo-block :title="$t('embeddedContent')">
+      <van-button
+        type="primary"
+        :text="$t('embeddedContent')"
+        style="margin-left: 16px;"
+        @click="showEmbedded = true"
+      />
+
+      <van-overlay :show="showEmbedded" @click="showEmbedded = false">
+        <div class="wrapper">
+          <div class="block" />
+        </div>
+      </van-overlay>
+    </demo-block>
   </demo-section>
 </template>
 
@@ -17,17 +32,37 @@
 export default {
   i18n: {
     'zh-CN': {
-      showOverlay: '显示遮罩层'
+      showOverlay: '显示遮罩层',
+      embeddedContent: '嵌入内容'
     },
     'en-US': {
-      showOverlay: 'Show Overlay'
+      showOverlay: 'Show Overlay',
+      embeddedContent: 'Embedded Content'
     }
   },
 
   data() {
     return {
-      show: false
+      show: false,
+      showEmbedded: false
     };
   }
 };
 </script>
+
+<style lang="less">
+.demo-overlay {
+  .wrapper {
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    height: 100%;
+  }
+
+  .block {
+    width: 120px;
+    height: 120px;
+    background-color: #fff;
+  }
+}
+</style>