jQuery scrollTop() doesn't seem to work in Safari or Chrome (Windows)

$(function() {
        $('#header').find('button').click(function(ev) {
          var button = $(this), target = $('div.' + button.attr('class'));
          var scroll = target.offsetParent().scrollTop(); 
          target.offsetParent().scrollTop(target.offset().top + scroll - 50);
        });
      });

html, body { height: 100%; padding: 0; }
      html { width: 100%; background-color: #222; overflow: hidden; margin: 0; }
      body { width: 40em; margin: 0px auto; background-color: white; position: relative; }
      #scrollContainer { overflow: auto; position:absolute; top: 0; height: 100%; width: 100%; }
      #header { position: absolute; top: 0px; height: 50px; width: 38.5em; background-color: white; z-index: 1; }
      #content { padding: 5px 14px 50px 5px;  }

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>
    <div id='header'> 
      Header Box
      <button class='A'>A</button> 
      <button class='B'>B</button> 
      <button class='C'>C</button> 
    </div> 
    <div id='scrollContainer'>
    <div id='content'> 
      <div style='height: 50px'> </div> 
      <div class='A'> 
        <h1>A</h1> 
        <p>My name is Boffer Bings. I was born of honest parents in one of the humbler walks of life, my father being a manufacturer of dog-oil and my mother having a small studio in the shadow of the village church, where she disposed of unwelcome babes. In my boyhood I was trained to habits of industry; I not only assisted my father in procuring dogs for his vats, but was frequently employed by my mother to carry away the debris of her work in the studio. In performance of this duty I sometimes had need of all my natural intelligence for all the law officers of the vicinity were opposed to my mother's business. They were not elected on an opposition ticket, and the matter had never been made a political issue; it just happened so. My father's business of making dog-oil was, naturally, less unpopular, though the owners of missing dogs sometimes regarded him with suspicion, which was reflected, to some extent, upon me. My father had, as silent partners, all the physicians of the town, who seldom wrote a prescription which did not contain what they were pleased to designate as _Ol. can._ It is really the most valuable medicine ever discovered. But most persons are unwilling to make personal sacrifices for the afflicted, and it was evident that many of the fattest dogs in town had been forbidden to play with me--a fact which pained my young sensibilities, and at one time came near driving me to become a pirate.
      </div> 
      <div class='B'> 
        <h1>B</h1> 
        <p> 
        Looking back upon those days, I cannot but regret, at times, that by indirectly bringing my beloved parents to their death I was the author of misfortunes profoundly affecting my future.
        <p> 
        One evening while passing my father's oil factory with the body of a foundling from my mother's studio I saw a constable who seemed to be closely watching my movements. Young as I was, I had learned that a constable's acts, of whatever apparent character, are prompted by the most reprehensible motives, and I avoided him by dodging into the oilery by a side door which happened to stand ajar. I locked it at once and was alone with my dead. My father had retired for the night. The only light in the place came from the furnace, which glowed a deep, rich crimson under one of the vats, casting ruddy reflections on the walls. Within the cauldron the oil still rolled in indolent ebullition, occasionally pushing to the surface a piece of dog. Seating myself to wait for the constable to go away, I held the naked body of the foundling in my lap and tenderly stroked its short, silken hair. Ah, how beautiful it was! Even at that early age I was passionately fond of children, and as I looked upon this cherub I could almost find it in my heart to wish that the small, red wound upon its breast--the work of my dear mother--had not been mortal.
      </div> 
      <div class='C'> 
        <h1>C</h1> 
        <p>It had been my custom to throw the babes into the river which nature had thoughtfully provided for the purpose, but that night I did not dare to leave the oilery for fear of the constable. "After all," I said to myself, "it cannot greatly matter if I put it into this cauldron. My father will never know the bones from those of a puppy, and the few deaths which may result from administering another kind of oil for the incomparable _ol. can._ are not important in a population which increases so rapidly." In short, I took the first step in crime and brought myself untold sorrow by casting the babe into the cauldron.
      </div> 
      <div style='height: 75em;'> </div> 
    </div> 
    </div>