apache - Website becomes weird. Updates out of sync? www difference?

Question

My website suddenly became weird
After I updated a css
I went to my website to see
www.xxx.com
The result was that the css was entered, assuming www.xxx.com /css.css Okay
After I entered it, I found that there was no update... The same happened after reorganizing
Make sure the upload was successful
So I changed to xxx.com/css.css and removed the www and sure enough, there was an update. ?
But when I go to www.xxx.com/css.css, it’s gone again.....
What kind of weird situation is this?
The weird thing is that there is no problem with the php code?
As long as there is an external connection, there will be problems. For example,

<link rel="stylesheet" type="text/css" href="css.css">
<script src="js.js"></script>

-_-

The same thing happens if you add this code

<META HTTP-EQUIV="PRAGMA" CONTENT="NO-CACHE">
<META HTTP-EQUIV="EXPIRES" CONTENT="0">
<META HTTP-EQUIV="CACHE-CONTROL" CONTENT="NO-CACHE">

There was no such problem before
As long as the js or css is saved and uploaded, it will be updated immediately...
Suddenly this problem occurred...
What's going on?

Answer 1

When quoting CSS files, try bringing a version number, href="xxx.css?v=2016"> like this

Answer 2

It should be cached, bring www, then press Ctrl+f5 to refresh and see