fixed skiplink button style, added ARIA role for skiplink buttons

resources/assets/stylesheets/less/skiplinks.less

@@ -23,13 +23,14 @@
 
 #skiplink_list {
     display: none;
-    button.skiplink {
-        border: 0;
-        background-color: #fff;
-        color: @base-color;
-        line-height: 1em;
-        margin-bottom: 0.1em;
-    }
+}
+
+button.skiplink {
+    border: 0;
+    background-color: #fff;
+    color: @base-color;
+    line-height: 1em;
+    margin-bottom: 0.1em;
 }
 
 body.enable-skiplinks {

templates/skiplinks.php

@@ -6,7 +6,7 @@
     <? foreach ($navigation as $nav) : ?>
         <li>
         <? if (mb_substr($url = $nav->getURL(), 0, 1) == '#') : ?>
-            <button class="skiplink" onclick="STUDIP.SkipLinks.setActiveTarget('<?= $url ?>');"><?= htmlReady($nav->getTitle()) ?></button>
+            <button class="skiplink" role="link" onclick="STUDIP.SkipLinks.setActiveTarget('<?= $url ?>');"><?= htmlReady($nav->getTitle()) ?></button>
         <? else : ?>
             <? if (is_internal_url($url)) : ?>
                 <a href="<?= URLHelper::getLink($url) ?>"><?= htmlReady($nav->getTitle()) ?></a>