Update shared navigation

Author: Jacek Gębal

docs/assets/topbar.css

@@ -38,10 +38,15 @@
   gap: 0.4rem;
 }
 
-#utplsql-topbar .utplsql-brand img {
-  height: 1.3rem;
-  width: auto;
+#utplsql-topbar .utplsql-brand-icon {
   display: block;
+  width: 1.3rem;
+  height: 1.3rem;
+  flex-shrink: 0;
+  background-image: url('icon-transparent.png');
+  background-repeat: no-repeat;
+  background-position: center;
+  background-size: contain;
 }
 
 #utplsql-topbar .utplsql-controls {

docs/assets/topbar.js

@@ -133,9 +133,9 @@
     brand.className = 'utplsql-brand';
     brand.href = BASE + '/';
 
-    var icon = document.createElement('img');
-    icon.src = BASE + '/assets/icon-transparent.png';
-    icon.alt = 'utPLSQL';
+    var icon = document.createElement('span');
+    icon.className = 'utplsql-brand-icon';
+    icon.setAttribute('aria-hidden', 'true');
     brand.appendChild(icon);
 
     var brandText = document.createElement('span');