Why doesn't @media request work?

Question

Sass

Hello everyone, the problem is that when I write some property in a media query, it is applied to the main layout, and not to the screen width that I specified
. For example, I wrote:

@media screen and (max-width:960px)
  header
    border: 1px solid red

And gave me in my compiled css file

header {
  border: 1px solid red
}

What could be the problem? Thank you all in advance!