Fix fallback styles. Update fallback and favicons.

src/_h5ai/public/css/inc/view/fallback.less

@@ -38,12 +38,14 @@
         }
     }
     .fb-i {
-        width: 24px;
+        width: 20px;
         padding-left: 12px;
 
         img {
-            width: 24px;
-            height: 24px;
+            width: 20px;
+            height: 20px;
+            position: relative;
+            top: -1px;
         }
     }
     .fb-n {
@@ -98,6 +100,7 @@ html.no-js, html.no-browser {
 
     #root {
         position: static;
+        overflow: auto;
     }
 
     #fallback, #fallback-hints {

src/_h5ai/public/images/favicon/favicon.svg

@@ -0,0 +1,3 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="16" height="16" viewBox="0 0 16 16">
+  <path fill="#555" d="M 1,2 1,14 15,14 15,4 9,4 7,2 z"/>
+</svg>