Add more color documentation, Add light buttons to docs

docs/documentation/elements/progress.html

@@ -41,10 +41,22 @@ meta:
 <progress class="progress is-large is-info" max="100">60%</progress>
 {% endcapture %}
 
+<div class="content">
+  <p>
+    The Bulma progress bar is a simple CSS class that styles the native <a href="https://developer.mozilla.org/en-US/docs/Web/HTML/Element/progress" target="_blank"><code>&lt;progress&gt;</code> HTML element</a>.
+  </p>
+</div>
+
 {% include elements/snippet.html content=progress %}
 
 {% include elements/anchor.html name="Colors" %}
 
+<div class="content">
+  <p>
+    The progress bar element is available in all the <strong>different colors</strong> defined by the <a href="{{ site.data.links.by_id.customize-variables.path }}"><code>$colors</code> Sass map</a>.
+  </p>
+</div>
+
 {% include elements/snippet.html content=progress_colors %}
 
 {% include elements/anchor.html name="Sizes" %}