断点 sass mixin

Question

Very very simple HTML SASS Why the breakpoint does not work and does not change the background and does not expand the size of the table HTML <table >nocontent</table>

CSS

$lg: 992px;
$xl: 1200px;
$xxl: 1400px;

$md : 768px;
@mixin for-up($size) {

  @media screen and (max-device-width: $size) {
    @content;

  }

  .table-main {
    height: 100vh;
    border: greenyellow solid;

    @include for-up($sm)
    {
      background-color: black;
      width: 100%;
      max-width: none;
    }
  }
}

Answer 1

$md : 768px;
@mixin for-up($size) {

  @media screen and (max-device-width: $size) {
    @content;

  }

.table-main {
  height: 100vh;
  border: greenyellow solid;

@include for-up($md)
  {
      background-color: black;
      width: 100%;
      max-width: none;
  }
  }
}

just add the proper starting and closing brackets, and than you good to go.