css is not applied.

<link rel="stylesheet" href="/style/top.css?after">
<link rel="stylesheet" href="/style/main.css?after">

I made a link like above, but no matter how much I modify css, it doesn't apply.
?after was also searched and used, but it didn't work after a while.
Rebooting the server itself does not apply;m;

The operating system that runs the P.S web server is Ubuntu 18.04 LTS.