update ads demo

packages/artplayer-plugin-ads/src/style.less

@@ -0,0 +1,16 @@
+.artplayer-plugin-ads {
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    position: absolute;
+    z-index: 150;
+    left: 0;
+    top: 0;
+    right: 0;
+    bottom: 0;
+    width: 100%;
+    height: 100%;
+    overflow: hidden;
+    color: #fff;
+    background-color: #000;
+}