Setup custom 404 page

There is a 404 page[1], but when we access wrong url, it will show apache default 404 page[2].

Something is wrong in here. we need fix configuration and also make small changes to existing page (it has different color)

[1] http://dubbo.apache.org/404.html
[2] http://dubbo.apache.org/404_NOT_FOUND

Start by locating the existing 404.html page and the Hugo website configuration involved in serving error pages. Compare the responses for /404.html and /404_NOT_FOUND, then verify that an invalid URL serves the custom page and that its color matches the requested design.

Written by the indexing model from the issue text.