Fix keyboard access for logout control

static/galene.css

@@ -133,15 +133,18 @@ a:focus {
     display: none;
 }
 
-.sidenav .user-logout a {
+.sidenav .user-logout button {
+    background: transparent;
+    border: 0;
     font-size: 1em;
     padding: 7px 0 0;
     color: #e4157e;
     cursor: pointer;
+    font: inherit;
     line-height: .7;
 }
 
-.sidenav .user-logout a:hover {
+.sidenav .user-logout button:hover {
     color: #ab0659;
 }
 

static/galene.html

@@ -165,10 +165,10 @@
               <span id="chpwspan" class="invisible"><a id="change-password" aria-label="Change password">Change password</a></span>
             </div>
             <div class="user-logout">
-              <a id="disconnectbutton" aria-label="Logout">
+              <button id="disconnectbutton" type="button" aria-label="Logout">
                 <span class="logout-icon"><i class="fas fa-sign-out-alt" aria-hidden="true"></i></span>
                 <span class="logout-text">Logout</span>
-              </a>
+              </button>
             </div>
           </div>
         </div>