add template for RouteNotFound

templates/error/route_not_found.html.slim

@@ -0,0 +1,4 @@
+p.error
+  'Sorry, this article does not exist. Maybe you want to go the
+  a(href=link_to('')) homepage
+  '  and see, if you can find your post there?

templates/stylesheet/index.css.scss

@@ -22,6 +22,7 @@ html {
   width: 100%;
   max-width: 1100px;
   margin: auto;
+  color: $normal_color;
 }
 
 code {
@@ -76,14 +77,17 @@ blockquote {
   }
 }
 
+#content {
+  padding-left: $standard-width;
+  padding-right: $standard-width;
+}
+
 a {
   text-decoration: none;
   color: $action-color;
 }
 
 .page {
-  margin-left: $standard-width;
-  margin-right: $standard-width;
   display: block;
   text-align: center;
   padding: $standard-width;
@@ -102,12 +106,18 @@ a {
     }
   }
 }
+
+.error {
+  padding: $standard-width;
+}
+
 #content, pre, blockquote {
   background-color: fade-out($alternate-color, 0.7);
 }
+
 article {
-  color: $normal_color;
-  padding: $standard-width;
+  padding-top: $standard-width;
+  padding-bottom: $standard-width;
   header {
     padding: $standard-width / 4;
     display: inline-block;