A CodePen by Cole Townsend.

index.html

<div class="container">
<a href="https://twitter.com/share" class="twitter-share-button tweet" data-text="{PostTitle} - {PostSummary}" data-via="{Text:Twitter Username}" data-hashtags="#{BlogName}">
    
       <span class="count">0</span>
       <span class="message">Tweet</span>
       
</a>
</div>

script.js

<script type="text/javascript">//<![CDATA[ 
$(window).load(function(){
var API_URL = "http://cdn.api.twitter.com/1/urls/count.json",
    TWEET_URL = "https://twitter.com/intent/tweet";
    
$(".tweet").each(function() {
    var elem = $(this),
    // Use current page URL as default link
    url = encodeURIComponent(elem.attr("data-url") || document.location.href),
    // Use page title as default tweet message
    text = elem.attr("data-text") || document.title,
    via = elem.attr("data-via") || "",
    related = encodeURIComponent(elem.attr("data-related")) || "",
    hashtags = encodeURIComponent(elem.attr("data-hashtags")) || "";
    
    // Set href to tweet page
    elem.attr({
        href: TWEET_URL + "?hashtags=" + hashtags + "&original_referer=" +
                encodeURIComponent(document.location.href) + "&related=" + related +
                "&source=tweetbutton&text=" + text + "&url=" + url + "&via=" + via,
        target: "_blank"
    });
    
    // Get count and set it as the inner HTML of .count
    $.getJSON(API_URL + "?callback=?&url=" + url, function(data) {
        elem.find(".count").html(data.count);
    });
});
});//]]>  
 
</script>

style.sass

@import "compass"
*
  border-sizing: border-box
  
html
  font-size: 62.5%

body
  font-size: 2rem
  font-family: "Brandon Grotesque"
  font-weight: bold

.container
  position: relative
  display: block
  margin: 0 auto


  .tweet
    text-decoration: none
    height: 2rem
    background: #e0e0e0
    color: #2a2a2a
    line-height: 2rem
    padding: 2rem
    position: relative
  
    .count, .message 
      line-height: 2rem
      position: relative
      top: 1rem