SASS why media queries don't work?

Question

css

There are simple styles, in chrome I resize, but the styles for the media query are not connected

body {
  background-color: $main-color;
  @media only screen and (max-width: 500px) {
    body {
        background-color: blue;

    }
  }
}

Answer 1

body {
  background-color: $main-color;
  @media only screen and (max-width: 500px) {
        background-color: blue;
  }
}