diff --git a/index.html b/index.html
index 8d0fc5ffce2dd34908123e9c0a8d4bb844cc9e34..7158d3fcf471d21c1dc0b9d15c9cb40108b504a3 100644
--- a/index.html
+++ b/index.html
@@ -75,6 +75,10 @@
     <div class="sharing">
       <a href="https://twitter.com/share" class="twitter-share-button" data-text="Check out 2048, a game where you join numbers to score high! #2048game" data-via="gabrielecirulli">Tweet</a>
       <script>!function(d,s,id){var js,fjs=d.getElementsByTagName(s)[0],p=/^http:/.test(d.location)?'http':'https';if(!d.getElementById(id)){js=d.createElement(s);js.id=id;js.src=p+'://platform.twitter.com/widgets.js';fjs.parentNode.insertBefore(js,fjs);}}(document, 'script', 'twitter-wjs');</script>
+      <span class="btc-donate">
+        <img src="meta/icon_bitcoin.png">Donate
+        <span class="address"><code>1Ec6onfsQmoP9kkL3zkpB6c5sA4PVcXU2i</code></span>
+      </span>
     </div>
   </div>
 
diff --git a/meta/icon_bitcoin.png b/meta/icon_bitcoin.png
new file mode 100644
index 0000000000000000000000000000000000000000..85e491b2c13938cf1074e402a15e80339e4552ed
Binary files /dev/null and b/meta/icon_bitcoin.png differ
diff --git a/style/main.css b/style/main.css
index 016732234c9914f50e450a6caedc6e7234aca356..f305c36fd7f9041c5053ced5f2c06ed7e4d345ac 100644
--- a/style/main.css
+++ b/style/main.css
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+/*
+Syntax error: Undefined mixin 'button'.
+        on line 492 of style/main.scss, in `button'
+        from line 492 of style/main.scss
+
+487: }
+488: 
+489: // Bitcoin donate button
+490: .btc-donate {
+491:   font-size: 14px;
+492:   @include button;
+493: }
+
+Backtrace:
+style/main.scss:492:in `button'
+style/main.scss:492
+/Users/gabriele/.rvm/gems/ruby-2.1.0/gems/sass-3.2.14/lib/sass/tree/visitors/perform.rb:253:in `visit_mixin'
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+/Users/gabriele/.rvm/gems/ruby-2.1.0/gems/sass-3.2.14/lib/sass/tree/visitors/perform.rb:100:in `visit'
+/Users/gabriele/.rvm/gems/ruby-2.1.0/gems/sass-3.2.14/lib/sass/tree/visitors/base.rb:53:in `block in visit_children'
+/Users/gabriele/.rvm/gems/ruby-2.1.0/gems/sass-3.2.14/lib/sass/tree/visitors/base.rb:53:in `map'
+/Users/gabriele/.rvm/gems/ruby-2.1.0/gems/sass-3.2.14/lib/sass/tree/visitors/base.rb:53:in `visit_children'
+/Users/gabriele/.rvm/gems/ruby-2.1.0/gems/sass-3.2.14/lib/sass/tree/visitors/perform.rb:109:in `block in visit_children'
+/Users/gabriele/.rvm/gems/ruby-2.1.0/gems/sass-3.2.14/lib/sass/tree/visitors/perform.rb:121:in `with_environment'
+/Users/gabriele/.rvm/gems/ruby-2.1.0/gems/sass-3.2.14/lib/sass/tree/visitors/perform.rb:108:in `visit_children'
+/Users/gabriele/.rvm/gems/ruby-2.1.0/gems/sass-3.2.14/lib/sass/tree/visitors/base.rb:37:in `block in visit'
+/Users/gabriele/.rvm/gems/ruby-2.1.0/gems/sass-3.2.14/lib/sass/tree/visitors/perform.rb:320:in `visit_rule'
+/Users/gabriele/.rvm/gems/ruby-2.1.0/gems/sass-3.2.14/lib/sass/tree/visitors/base.rb:37:in `visit'
+/Users/gabriele/.rvm/gems/ruby-2.1.0/gems/sass-3.2.14/lib/sass/tree/visitors/perform.rb:100:in `visit'
+/Users/gabriele/.rvm/gems/ruby-2.1.0/gems/sass-3.2.14/lib/sass/tree/visitors/base.rb:53:in `block in visit_children'
+/Users/gabriele/.rvm/gems/ruby-2.1.0/gems/sass-3.2.14/lib/sass/tree/visitors/base.rb:53:in `map'
+/Users/gabriele/.rvm/gems/ruby-2.1.0/gems/sass-3.2.14/lib/sass/tree/visitors/base.rb:53:in `visit_children'
+/Users/gabriele/.rvm/gems/ruby-2.1.0/gems/sass-3.2.14/lib/sass/tree/visitors/perform.rb:109:in `block in visit_children'
+/Users/gabriele/.rvm/gems/ruby-2.1.0/gems/sass-3.2.14/lib/sass/tree/visitors/perform.rb:121:in `with_environment'
+/Users/gabriele/.rvm/gems/ruby-2.1.0/gems/sass-3.2.14/lib/sass/tree/visitors/perform.rb:108:in `visit_children'
+/Users/gabriele/.rvm/gems/ruby-2.1.0/gems/sass-3.2.14/lib/sass/tree/visitors/base.rb:37:in `block in visit'
+/Users/gabriele/.rvm/gems/ruby-2.1.0/gems/sass-3.2.14/lib/sass/tree/visitors/perform.rb:128:in `visit_root'
+/Users/gabriele/.rvm/gems/ruby-2.1.0/gems/sass-3.2.14/lib/sass/tree/visitors/base.rb:37:in `visit'
+/Users/gabriele/.rvm/gems/ruby-2.1.0/gems/sass-3.2.14/lib/sass/tree/visitors/perform.rb:100:in `visit'
+/Users/gabriele/.rvm/gems/ruby-2.1.0/gems/sass-3.2.14/lib/sass/tree/visitors/perform.rb:7:in `visit'
+/Users/gabriele/.rvm/gems/ruby-2.1.0/gems/sass-3.2.14/lib/sass/tree/root_node.rb:20:in `render'
+/Users/gabriele/.rvm/gems/ruby-2.1.0/gems/sass-3.2.14/lib/sass/engine.rb:315:in `_render'
+/Users/gabriele/.rvm/gems/ruby-2.1.0/gems/sass-3.2.14/lib/sass/engine.rb:262:in `render'
+/Users/gabriele/.rvm/gems/ruby-2.1.0/gems/sass-3.2.14/lib/sass/plugin/compiler.rb:362:in `update_stylesheet'
+/Users/gabriele/.rvm/gems/ruby-2.1.0/gems/sass-3.2.14/lib/sass/plugin/compiler.rb:203:in `block in update_stylesheets'
+/Users/gabriele/.rvm/gems/ruby-2.1.0/gems/sass-3.2.14/lib/sass/plugin/compiler.rb:201:in `each'
+/Users/gabriele/.rvm/gems/ruby-2.1.0/gems/sass-3.2.14/lib/sass/plugin/compiler.rb:201:in `update_stylesheets'
+/Users/gabriele/.rvm/gems/ruby-2.1.0/gems/sass-3.2.14/lib/sass/plugin/compiler.rb:283:in `block in watch'
+/Users/gabriele/.rvm/gems/ruby-2.1.0/gems/sass-3.2.14/vendor/listen/lib/listen/multi_listener.rb:108:in `call'
+/Users/gabriele/.rvm/gems/ruby-2.1.0/gems/sass-3.2.14/vendor/listen/lib/listen/multi_listener.rb:108:in `on_change'
+/Users/gabriele/.rvm/gems/ruby-2.1.0/gems/sass-3.2.14/vendor/listen/lib/listen/multi_listener.rb:117:in `block in initialize_adapter'
+/Users/gabriele/.rvm/gems/ruby-2.1.0/gems/sass-3.2.14/vendor/listen/lib/listen/adapter.rb:198:in `call'
+/Users/gabriele/.rvm/gems/ruby-2.1.0/gems/sass-3.2.14/vendor/listen/lib/listen/adapter.rb:198:in `report_changes'
+/Users/gabriele/.rvm/gems/ruby-2.1.0/gems/sass-3.2.14/vendor/listen/lib/listen/adapter.rb:210:in `poll_changed_dirs'
+/Users/gabriele/.rvm/gems/ruby-2.1.0/gems/sass-3.2.14/vendor/listen/lib/listen/adapters/darwin.rb:38:in `block in start'
+*/
+body:before {
+  white-space: pre;
+  font-family: monospace;
+  content: "Syntax error: Undefined mixin 'button'.\A         on line 492 of style/main.scss, in `button'\A         from line 492 of style/main.scss\A \A 487: }\A 488: \A 489: // Bitcoin donate button\A 490: .btc-donate {\A 491:   font-size: 14px;\A 492:   @include button;\A 493: }"; }
diff --git a/style/main.scss b/style/main.scss
index 9570ff3cf2bfff71b64713e5976e114f7816b941..404ac76ede2fe9d64731bf0e4f7353358ecbe155 100644
--- a/style/main.scss
+++ b/style/main.scss
@@ -485,3 +485,8 @@ hr {
     }
   }
 }
+
+// Bitcoin donate button
+.btc-donate {
+  font-size: 14px;
+}