This demo site page shows how to user Site Search 360 in an overlay mode when search results are displayed in a popup on top of your pages. View the to check the configuration.

window.ss360Config = {
   siteId: 'spoonacular.com', /* Replace with your site id */
   searchBox: {
      selector: '#searchBox' /* Replace with the css selector of your search box */
   },
   suggestions: {
   source: {
      queryBased: {
         content: [{
            type: 'resultGroup',
            dataPoints: [
               { key: 'Cost', type: 'value' },
               { key: 'Calories', type: 'chip' },
            ]	  
         }]
      }
   }
};