feat: Corner ribbon pattern

contents/_includes/patterns/corner-ribbon.njk

@@ -0,0 +1,6 @@
+<div class="corner-ribbon">
+    <div class="corner-ribbon__inner">
+        <div class="corner-ribbon__ribbon">
+        </div>
+    </div>
+</div>

contents/corner-ribbon.md

@@ -0,0 +1,65 @@
+---
+layout: layouts/post.njk
+title: Corner ribbon
+description: Create a corner ribbon with CSS flexbox
+keywords: css flexbox, css ribbon
+---
+
+## HTML
+
+```html
+<div class="corner-ribbon">
+    <!-- The container -->
+    <div class="corner-ribbon__inner">
+        <!-- The ribbon -->
+        <div class="corner-ribbon__ribbon">
+        </div>
+    </div>
+</div>
+```
+
+## CSS
+
+```css
+.corner-ribbon {
+    position: relative;
+}
+
+.corner-ribbon__inner {
+    /* Displayed at the top left corner */
+    left: 0px;
+    position: absolute;
+    top: 0px;
+
+    /* Size */
+    height: 4rem;
+    width: 4rem;
+
+    /* Hide the part of its children which is displayed outside */
+    overflow: hidden;
+}
+
+.corner-ribbon__ribbon {
+    /* Position */
+    left: 1rem;
+    position: absolute;
+    top: 1rem;
+
+    /* Size */
+    height: 1.5rem;
+    width: 5.656rem;
+
+    /* Displayed diagonally */
+    transform: translate(-38px, -8px) rotate(-45deg);
+
+    /* Background color */
+    background-color: rgba(0, 0, 0, 0.3);
+
+    /* Centerize the text content */
+    text-align: center;
+}
+```
+
+{% demo %}
+{% include "patterns/corner-ribbon.njk" %}
+{% enddemo %}

contents/index.njk

@@ -79,6 +79,12 @@ eleventyExcludeFromCollections: true
                     <div class="pattern__title">Cookie banner</div>
                 </a>
             </div>
+            <div class="pattern__item">
+                <a class="pattern__link" href="/corner-ribbon/">
+                    <div class="pattern__cover">{% include "patterns/corner-ribbon.njk" %}</div>
+                    <div class="pattern__title">Corner ribbon</div>
+                </a>
+            </div>
         </div>
     </div>