Add code highlighting and make minor style changes

themes/vanilla/assets/scss/style.scss

@@ -32,6 +32,13 @@ code {
   background-color: #f0f0f0;
 }
 
+pre code {
+    display: block;
+    padding: 0.5em;
+    overflow-x: auto;
+    background-color: #f0f0f0;
+}
+
 .container {
   margin: auto;
   width: 100%;
@@ -61,13 +68,13 @@ code {
   }
 }
 
-.navbar {
+nav {
   background-color: $primary-color;
   width: 100%;
   margin: 1em 0px 1em 0px;
 }
 
-.navbar-button {
+nav a {
   padding: .75em;
   text-decoration: none;
   color: white;
@@ -113,6 +120,7 @@ h5 {
 h6 {
   font-size: 1.0rem;
 }
+
 a {
   color: $primary-color-dark;
   text-decoration: none;