feat(WebexWidget): add theme selector on the widgets demo page

demo/WebexMeetingWidgetDemo.jsx

@@ -1,13 +1,14 @@
 import React, {useState} from 'react';
 import PropTypes from 'prop-types';
-import {Button, Input} from '@momentum-ui/react';
+import {Button, Input, Select, SelectOption} from '@momentum-ui/react';
 import './WebexMeetingWidgetDemo.scss';
 
 import {WebexMeetingWidget} from '../src';
 
 export default function WebexMeetingWidgetDemo({token}) {
   const [destination, setDestination] = useState('');
   const [displayWidget, setDisplayWidget] = useState(false);
+  const [theme, setTheme] = useState('dark');
 
   const displayButtonEnabled = token && destination && !displayWidget;
 
@@ -21,6 +22,11 @@ export default function WebexMeetingWidgetDemo({token}) {
     setDisplayWidget(false);
   };
 
+  const handleChangeTheme = (selectedOptions) => {
+    const selectedTheme = selectedOptions[0].value;
+    setTheme(selectedTheme);
+  };
+
   return (
     <React.Fragment>
       <h3>Webex Meeting Widget</h3>
@@ -47,12 +53,17 @@ export default function WebexMeetingWidgetDemo({token}) {
         <Button disabled={!displayWidget} onClick={handleHideMeetingWidget} ariaLabel="Remove Meeting Widget">
           Remove Meeting Widget
         </Button>
+        <div className="webex-theme-selector">Theme</div>
+        <Select defaultValue="Dark" onSelect={handleChangeTheme}>
+          <SelectOption value="dark" label="Dark" />
+          <SelectOption value="light" label="Light" />
+        </Select>
       </form>
       {token && destination && displayWidget && (
         <WebexMeetingWidget
           accessToken={token}
           meetingDestination={destination}
-          className="webex-meeting-widget-demo fluid-height"
+          className={`webex-meeting-widget-demo fluid-height wxc-theme-${theme}`}
         />
       )}
     </React.Fragment>

demo/WebexMeetingWidgetDemo.scss

@@ -2,3 +2,8 @@
   width: 100%;
   min-height: 400px;
 }
+
+.webex-theme-selector {
+  margin-top: 8px;
+  color: #121212;
+}