Streets only styling for Mapbox Studio

old_roads.css

    [class='motorway'] {
      line-join:round;
      line-color: @motorway_case;
      #road { line-cap: round; }
      #tunnel { line-dasharray:3,2; }
      [zoom>=6]  { line-width:0.4; }
      [zoom>=7]  { line-width:0.6; }
      [zoom>=8] { line-width:1.5; }
      [zoom>=9] { line-width: 1.75; }
      [zoom>=10]  { line-width:2; }
      [zoom>=13] { line-width:3.5;  }
      [zoom>=14] { line-width:5; }
      [zoom>=15] { line-width:7; }
      [zoom>=16] { line-width:9; }
    }
    [class='motorway_link'][zoom>=13] {
      line-join:round;
      line-color: @motorway_case;
      #road { line-cap: round; }
      #tunnel { line-dasharray:3,2; }
      [zoom>=13] { line-width:1; }
      [zoom>=14] { line-width:3; }
      [zoom>=15] { line-width:5; }
      [zoom>=16] { line-width:6.5; }
    }
    [class='main'] {
      line-join:round;
      line-color: @main_case;
      #road { line-cap: round; }
      #tunnel { line-dasharray:3,2; }
      [zoom=7] { line-width: 0; }
      [zoom>=12] { line-width: 0; }
      [zoom=13] { line-width:2.5; }
      [zoom=14] { line-width:4; }
      [zoom=15] { line-width:5; }
      [zoom>=16] { line-width:8; }
    }

style.css

@land: #f6f2ec;

@minor_color: #1d1d1d;
@major_color: #000;
@default_color: "red";

Map {
  background-color: @land;
}


#road, #bridge, #tunnel {
  line-join:round;
  line-cap: round;
  line-width:0.5;
  line-color:@minor_color;
  [class='major_rail'] {
    line-opacity:0.0;
    line-width:0.0;
  }
  [class='rail'] {
    line-opacity:0.0;
    line-width:0.0;
  }
  [class='footway '] {
    line-opacity:0.0;
    line-width:0.0;
  }
  [class='cycleway'] {
    line-opacity:0.0;
    line-width:0.0;
  }
  [class='secondary '] {
    line-color:@major_color;
    line-width:0.6;
  }
  [class='main'] {
    line-color:@major_color;
    line-width:1.0;
  }
  [class='trunk'] {
    line-color:@major_color;
    line-width:1.5;
  }
  [class='primary'] {
    line-color:@major_color;
    line-width:1.5;
  }
  [class='motorway'] {
    line-color:@major_color;
    line-width:1.5;
  }
}