Add a link to the top of the page in galleries

Herisson/gallery.html.j2

                 </div>
             </div>
         </main>
+
+        <a class="to-the-top" href="#">Haut de page</a>
     </body>
 </html>

Herisson/style/main.css

     width: 100%;
     height: 12rem;
 }
+
+.to-the-top {
+    position: fixed;
+    bottom: 2rem;
+    right: 2rem;
+
+    padding: .25rem .5rem;
+
+    color: #fff;
+    text-decoration: none;
+    font-size: .9rem;
+
+    background-color: #404c9e;
+    border-radius: .25rem;
+
+    transition: background .2s ease-in-out;
+}
+.to-the-top:hover {
+    color: #fff;
+
+    background-color: #7586f0;
+}