docs: function initVideoFallback(opt_config) {
    var videoSelector = (opt_config && opt_config.videoSelector)
        || defaultConfig.fallbackVideoSelector;
    var imageSelector = (opt_config && opt_config.imageSelector)
        || defaultConfig.fallbackImageSelector;
    var breakpoint = (opt_config && opt_config.breakpoint)
        || defaultConfig.breakpoint;
  
    var hidden = {'display': 'none !important'};
    var rules = {};
    if (canPlayVideo()) {
      rules[imageSelector] = hidden;
    } else {
      rules[videoSelector] = hidden;
    }
  
    if (!breakpoint) {
      ui.createStyle(rules);
    } else {
      var minScreenQuery = '(min-width: ' + breakpoint + 'px)';
      ui.createStyle(rules, minScreenQuery);
      var smallerBreakpoint = breakpoint - 1;
      var maxScreenQuery = '(max-width: ' + smallerBreakpoint + 'px)';
      rules = {};
      rules[videoSelector] = hidden;
      ui.createStyle(rules, maxScreenQuery);
    }
  }