feat(404): changed the error page to be generic and used with a custom go server

assets/scss/style.scss

@@ -351,13 +351,13 @@ table {
   margin: auto;
   font-size: 1.2rem;
 
-  &.error-404 {
+  &.http-error {
     flex-direction: row;
     line-height: normal;
   }
 }
 
-#spotlight.error-404 > #home-center {
+#spotlight.http-error > #home-center {
   align-self: center;
   flex-direction: row;
 }
@@ -372,7 +372,7 @@ p.img-404 {
   }
 }
 
-.banner-404 {
+.banner-error {
   margin-left: 2em;
 
   h1 {
@@ -384,7 +384,7 @@ p.img-404 {
     margin-top: 0;
   }
 
-  .btn-404 {
+  .btn-http-error {
     font-size: .8em;
 
     a {
@@ -909,13 +909,13 @@ a.footnote-ref {
     }
   }
 
-  #spotlight.error-404 {
+  #spotlight.http-error {
     flex-direction: row;
     flex-grow: 1;
     text-align: center;
     align-self: center;
 
-    .banner-404 {
+    .banner-error {
       margin: 0;
     }
   }