Add from and until mixins docs

docs/bulma-docs.scss

@@ -249,3 +249,11 @@ $navbar-breakpoint: $tablet;
 @import "./_sass/global/cc";
 
 @import "./_sass/examples/mixins";
+
+.my-element {
+  background: red;
+
+  @include from(1280px) {
+    background: blue;
+  }
+}

docs/css/bulma-docs.css

@@ -22925,4 +22925,14 @@ fieldset[disabled] .bulma-control-mixin {
   color: white;
 }
 
+.my-element {
+  background: red;
+}
+
+@media screen and (min-width: 1280px) {
+  .my-element {
+    background: blue;
+  }
+}
+
 /*# sourceMappingURL=bulma-docs.css.map */

docs/documentation/utilities/responsive-mixins.html

@@ -15,10 +15,137 @@ breadcrumb:
   <p>
     Bulma is <strong>responsive by default</strong>. <a href="{{ site.url}}/overview/responsiveness/">Learn more about Bulma's responsiveness</a>.
   </p>
+</div>
 
-  <div class="content">
-     By having <strong>4 breakpoints</strong> and supporting <strong>5 screen sizes</strong>, Bulma can support a lot of different setups. To simplify your development process, the framework provides several <strong>responsive mixins</strong> that you can use to create a <strong>responsive design</strong>:
-  </div>
+{% include elements/anchor.html name="from() and until() mixins" %}
+
+<div class="content">
+  <p>
+    Responsiveness in CSS is based on <strong>media queries</strong> (see <a href="https://developer.mozilla.org/en-US/docs/Web/CSS/Media_Queries/Using_media_queries" target="_blank">MDN documentation</a>).
+  </p>
+
+  <p>
+    Bulma provides <strong>2 useful responsive mixins:</strong>
+  </p>
+
+  <ul>
+    <li>
+      {% include elements/snippet-inline.html content="@mixin from($breakpoint)" %} to target devices with a screen <em>wider</em> than or equal to the breakpoint
+    </li>
+    <li>
+      {% include elements/snippet-inline.html content="@mixin until($breakpoint)" %} to target devices with a screen <em>narrower</em> than the breakpoint
+    </li>
+  </ul>
+
+  <p>Their usage is very simple:</p>
+</div>
+
+{% include elements/anchor-bis.html name="from()" %}
+
+<div class="content">
+  <p>
+    The <code>from()</code> mixin has a single parameter which sets the <strong>screen width</strong> from which the styles it contains will be applied:
+  </p>
+</div>
+
+<p class="title is-6">Sass source</p>
+
+{% highlight sass %}.my-element {
+  background: red;
+
+  @include from(1280px) {
+    background: blue;
+  }
+}{% endhighlight %}
+
+<p class="title is-6">CSS output</p>
+
+{% highlight css %}.my-element {
+  background: red;
+}
+
+@media screen and (min-width: 1280px) {
+  .my-element {
+    background: blue;
+  }
+}{% endhighlight %}
+
+<div class="content">
+  <p>
+    For screens with a width of 1279px or less, the element's background will be <strong style="color: red;">red</strong>.
+    <br>
+    For screens 1280px-wide or more, the element's background will be <strong style="color: blue;">blue</strong>.
+  </p>
+</div>
+
+{% include elements/anchor-bis.html name="until()" %}
+
+<div class="content">
+  <p>
+    The <code>until()</code> mixin has a single parameter which sets the <strong>screen width (minus <code>1px</code>)</strong> until which the styles it contains will be applied.
+  </p>
+
+  <p>
+    This means that if you set a value of <code>1280px</code>, the styles will be applied on a screen width of <code>1279px</code> but <strong>not</strong> on a screen width of <code>1280px</code>.
+  </p>
+
+  <p>
+    The reason for this <strong>1px offset</strong> is to allow you to use both <code>from()</code> and <code>until()</code> with the <strong>same breakpoint value</strong>. This leaves <strong>no gap</strong> between the 2 sets of rules.
+  </p>
+</div>
+
+<p class="title is-6">Sass source</p>
+
+{% highlight sass %}$breakpoint: 1280px;
+
+.my-element {
+  @include until($breakpoint) {
+    background: green;
+  }
+
+  @include from($breakpoint) {
+    background: orange;
+  }
+}{% endhighlight %}
+
+<p class="title is-6">CSS output</p>
+
+{% highlight css %}@media screen and (max-width: 1279px) {
+  .my-element {
+    background: green;
+  }
+}
+
+@media screen and (min-width: 1280px) {
+  .my-element {
+    background: orange;
+  }
+}{% endhighlight %}
+
+<div class="content">
+  <p>
+    For screens with a width of 1279px or less, the element's background will be <strong style="color: green;">green</strong>.
+    <br>
+    For screens 1280px-wide or more, the element's background will be <strong style="color: orange;">orange</strong>.
+  </p>
+</div>
+
+{% include elements/anchor.html name="Named mixins" %}
+
+<div class="content">
+  <p>
+    By having <strong>4 breakpoints</strong> and supporting <strong>5 screen sizes</strong>, Bulma can support a lot of different setups.
+  </p>
+</div>
+
+<div class="content">
+  While you could use the mixins {% include elements/snippet-inline.html content="@include from()" %} and {% include elements/snippet-inline.html content="@include until()" %}, Bulma provides <strong>quick shortcuts</strong> with <strong>11 named mixins</strong>.
+</div>
+
+<div class="content">
+  <p>
+      These <strong>responsive mixins</strong> are named after the screen sizes and breakpoints used in Bulma, so that you can use them to create a <strong>responsive designs</strong>:
+  </p>
 </div>
 
 {% capture inc-mobile %}