Update app.less

Author: huangshuwei

examples/src/comp/app.less

@@ -90,6 +90,8 @@
                             .switch-version-dropdown-pannel {
                                 position: absolute;
                                 display: none;
+                                max-height: 300px;
+                                overflow: auto;
                                 margin-top: 10px;
                                 padding: 8px 0;
                                 border: 1px solid #d1dbe5;