Emulate position:fixed on a div to keep it locked, vertically, inside the browser viewport. Designed for tiny sidebar-style content.Add class 'bump-me-down' to any floated div & it'll add padding to the top to make it fit.

bumpMeDown.js

/// Bump-down a div to fit (position:fixed style) inside a browser
$(function(){
  if($('.bump-me-down').length > 0) {
    $(window).on('scroll process-bump-me-downs resize', function(){
      var scrollTop = $(window).scrollTop();
      var defaultPad = 20;
      $('.bump-me-down').each(function(){
        var thisOffset = $(this).offset().top;
        if($(this).data('bumpOffset')) {
          thisOffset -= $(this).data('bumpOffset');
        }
        var thisHeight = $(this).outerHeight(true);
        if(scrollTop > thisOffset - defaultPad) {
          var parentHeight = $(this).parent().height();
          var desiredPad = defaultPad + (scrollTop - thisOffset);
          var maxPad = parentHeight - thisHeight;
          var offsetToSet = Math.round(Math.min(desiredPad, maxPad));
          $(this).addClass('is-bumped').data('bumpOffset', offsetToSet).css('transform', 'translateY(' + offsetToSet + 'px)');
        } else {
          $(this).filter('.is-bumped').removeClass('is-bumped').data('bumpOffset', 0).css('transform', '');
        }
      });
    }).trigger('process-bump-me-downs');
  }
});