Use nice URIs and set up redirects for the old ones

.htaccess

@@ -1,3 +1,14 @@
-ErrorDocument 404 /main.php?page=404
-DirectoryIndex maincg.php main.php index.php start.html index.html
-Options -Indexes
+RewriteEngine on
+
+RewriteCond &%{QUERY_STRING} &page=([^&]+) [NC]
+RewriteRule ^(maincg\.php)?$ %1.html [R=301,QSD,L]
+
+RewriteRule pages/(.*)\.php $1.html [R=301,L]
+
+RewriteRule ^cyklogaining.html$ / [R=301,L]
+
+RewriteCond %{REQUEST_FILENAME} !-f
+RewriteCond %{REQUEST_FILENAME} !-d
+RewriteRule !\.(pdf|js|ico|gif|jpg|jpeg|png|webp|svg|css|rar|zip|7z|tar\.gz|map|eot|ttf|otf|woff|woff2)$ index.php [L]
+
+Options -Indexes