This demo site page shows how to use Site Search 360 in fullscreen mode. 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 */
   },
   results: {
      fullScreenConfig: {
         trigger: '#ss360-search-trigger',
         caption: 'Search this demo site'
     }
   },
   layout: {
      mobile: {
         type: 'grid'
      },
      desktop: {
         type: 'grid'
      }
   }
};