CSS3 moon shape
<p>I am trying to create a button like this:</p>

<p><a href="https://i.stack.imgur.com/U2H1o.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/U2H1o.jpg" alt="enter image description here"></a></p>

<p>I dont know how to create a light moon shape over the top of the button.</p>

<p>This is still far off: <a href="https://jsfiddle.net/wgnp9ygh/2/" rel="nofollow noreferrer">Fiddle Demo</a>.</p>

<pre><code>.moon {
   width: 50px;
   height: 50px;
   border-radius: 50%;
   box-shadow: 15px 15px 0 0 green;
}
</code></pre>