How to style Facebook and Twitter share buttons?

I have added Facebook share button and it forks fine, but I have problems with style. I want to change button style, make my custom style. I have tried to put style in my own style.css calling classes that I find using Fire Bug but when I put my own style using those classes nothing happens, it's like I haven't add any style.

This is how my code look like

<script>
      window.fbAsyncInit = function() {
        FB.init({
          appId      : 'your-app-id',
          xfbml      : true,
          version    : 'v2.1'
        });
      };

      (function(d, s, id){
         var js, fjs = d.getElementsByTagName(s)[0];
         if (d.getElementById(id)) {return;}
         js = d.createElement(s); js.id = id;
         js.src = "//connect.facebook.net/en_US/sdk.js";
         fjs.parentNode.insertBefore(js, fjs);
       }(document, 'script', 'facebook-jssdk'));
    </script>

HTML:

<div class="fb-share-button" data-href="http://localhost/dfs/jersey.php" data-layout="button_count"></div>

Can anybody help me please?

Also I have same problem with Twitter button.

Thank you.