I am planning to replace WordPress on my site with custom HTML/CSS/JS, and I'm trying to check my .htaccess file will work. It is working, as I was able to change the directory index with it, but for some reason ErrorDocument 404 /errors/404.html does not work. Instead, when I type a bogus URL, the standard browser 404 message appears.

I have tried just having that line in the htaccess file. I think it may be due to the WordPress folder, which I will delete once the new site is ready. Is this the problem?