Show the "error 404" message on top

src/error.ml

@@ -12,9 +12,20 @@ br, hr {
   display: none;
 }
 h1 {
-  color: rgba(255,255,255,.75);
-  margin: 1.5ex;
   text-align: center;
+  position: fixed;
+  color: black;
+  left: 0;
+  right: 0;
+  top: 40%;
+  z-index: 1;
+  font-family: helvetica;
+  text-transform: uppercase;
+  font-size: 6vmin;
+  font-weight: bold;
+  mix-blend-mode: overlay;
+  user-select: none;
+  text-shadow: 0 0 .7vmin black;
 }
 footer {
   position: fixed;