Make a group of buttons fill the whole width of the parent div
<p>I have a small panel with a width of <code>360px</code>. At the top of the panel, there is a navigation bar consisting of currently 3 buttons (the number should not matter though). I want the buttons to fill out the whole width of the div and take up more or less space depending on the length of the word inside. Currently, I only know how to set the width of the buttons to a value, but then if I add a button the values would need to be changed manually.</p>

<p><img src="https://i.stack.imgur.com/XsNmh.png" alt="what it currently looks like"></p>

<p>this is what I have now, but obviously it looks horrible. How can I make the first button less wide, the second button wider and have all three buttons together take up the whole width of the panel?</p>

<p>Here is my code:</p>

<p>HTML:</p>

<pre class="lang-html prettyprint-override"><code>&lt;!DOCTYPE html&gt;
&lt;html&gt;
&lt;head&gt;
    &lt;title&gt;TEST&lt;/title&gt;
    &lt;link type="text/css" rel="stylesheet" href="test.css"/&gt;
&lt;/head&gt;
&lt;body&gt;
    &lt;div class="panel"&gt;
        &lt;ul class="nav"&gt;
            &lt;li class="buttons"&gt;SHORT&lt;/li&gt;
            &lt;li class="buttons"&gt;LOOOOOOOOOOONG&lt;/li&gt;
            &lt;li class="buttons"&gt;...&lt;/li&gt;
        &lt;/ul&gt;
    &lt;/div&gt;
&lt;/body&gt;
&lt;/html&gt;
</code></pre>

<p>CSS:</p>

<pre class="lang-css prettyprint-override"><code>.panel {
    background-color: grey;
    width: 360px;
    height: 600px;
    position: relative;
    border: 1px solid black;
}

.nav {
    padding: 0;
    margin: 0;
}

.buttons {
    float: left;
    display: block;
    padding: 0px 20px;
    height: 40px;
    width: 60px;
    background-color: #666666;
    border-right: 1px solid black;
    border-bottom: 1px solid black;
    text-align: center;
    line-height: 40px;
}
</code></pre>