tidy up notes index page

public/css/base.css

@@ -201,11 +201,11 @@ figcaption {
 
 /** Navigation bar */
 
-nav {
+.navbar {
   margin-block: var(--spacing-block-sm);
 }
 
-nav ul {
+.navbar ul {
   grid-column: media-start / content-end;
   display: flex;
   justify-content: center;
@@ -215,12 +215,12 @@ nav ul {
 }
 
 @media (min-width: 36rem) {
-  nav {
+  .navbar {
     display: grid;
     grid-template-columns: subgrid;
   }
 
-  nav ul {
+  .navbar ul {
     justify-content: end;
   }
 }
@@ -296,3 +296,21 @@ pre code {
   padding-inline: var(--spacing-inline-xs);
   background-color: var(--color-primary-fg-accent);
 }
+
+
+.visually-hidden {
+    position: absolute;
+      width: 1px;
+      height: 1px;
+      margin: -1px;
+      border: 0;
+      padding: 0;
+
+      white-space: nowrap;
+      clip-path: inset(100%);
+      clip: rect(0 0 0 0);
+      overflow: hidden;
+
+      outline: none;
+      outline-offset: 0;
+}