How to attach CSS file to xml file format?

This is my first xml file testing with a css file. I was following a tutorial on youtube. There was one difference between output I got and the output in the video

When this guys is creating a xml file which is:

<?xml version="1.0" encoding="utf-8"?>
<first>
    This is first XML here
</first>

and open this file in browser, he gets content which is

<first>
    This is first XML here
</first>

but when I did same thing I got this in the browser

This is first XML here

I ignored this difference and then I added css file:

I created a style.css file in same folder:

first
(
    display : block;
    font-family : Arial;
    font-size : large;
    color : Blue;
)

And then I changed xml file to this:

<?xml version="1.0" encoding="utf-8"?>
<?xml-stylesheet type="text/css" href="style.css"?>
<first>
    This is first XML here
</first>

but output in the browser is same as before. It seems css does not changing anything. I am using Xmplify XML Editor on Mac OS and also I used Safari and google chrome for the output but neither of them worked. I appreciate if anyone can help me with that.