Changed the display absolute to flex for both 404 and 500 page

public/404.html

@@ -16,19 +16,14 @@
 
     body {
       margin: 0;
+      height: 100vh;
+      display: flex;
+      align-items: center;
+      justify-content: center;
+      background: white;
       font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
       color: #555;
       text-align: center;
-      background: white;
-    }
-
-    div {
-      position: absolute;
-      top: 50%;
-      left: 0;
-      right: 0;
-      margin-top: -5em;
-      padding: 0 1em;
     }
 
     h1 {
@@ -41,7 +36,7 @@
     }
 
     p {
-      margin: 1.5em 0 0;
+      margin: 1.5em 0;
       line-height: 1.8;
       font-weight: 300;
     }

public/500.html

@@ -16,21 +16,16 @@
 
     body {
       margin: 0;
+      height: 100vh;
+      display: flex;
+      align-items: center;
+      justify-content: center;
       font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
       color: #555;
       text-align: center;
       background: white;
     }
 
-    div {
-      position: absolute;
-      top: 50%;
-      left: 0;
-      right: 0;
-      margin-top: -6em;
-      padding: 0 1em;
-    }
-
     h1 {
       margin: 0;
       line-height: 1;
@@ -41,7 +36,7 @@
     }
 
     p {
-      margin: 1.5em 0 0;
+      margin: 1.5em 0;
       line-height: 1.8;
       font-weight: 300;
     }