If i make a file called vps.html it marks my file as red and if I call it anyother name it marks it green

As the title says,

When I try to make a file called vps.html, it marks it red like this: https://gyazo.com/abb0aed01e0ba72bee733a9cfaff1be6 

and if I type a

<footer>

tag, it says: "Element footer is not allowed here"

But if I call it vpsplans.html, it seems all right.

What is the problem?

Sincerely,

Doron