How to make a background notification when the site starts?

Question

PHP

How to make an adaptive background notification on the first launch of the site?
Example:

Answer 1

function get_location() {
  if (Modernizr.geolocation) {
    navigator.geolocation.getCurrentPosition(show_map);
  } else {
   // Нет встроенной поддержки
  }
}

htmlbook.ru/html5/geolocation

Answer 2

See how it's done in the twentyseventeen off -topic .
There is icon-functions.php file