atom/packages/atom-light-syntax/styles/editor.less

atom-text-editor {
  background-color: @syntax-background-color;
  color: @syntax-text-color;

  .invisible-character {
    color: @syntax-invisible-character-color;
  }

  .indent-guide {
    color: @syntax-indent-guide-color;
  }

  .wrap-guide {
    background-color: @syntax-wrap-guide-color;
  }

  .gutter {
    color: @syntax-gutter-text-color;
    background: @syntax-gutter-background-color;
  }

  .gutter .line-number.folded,
  .gutter .line-number:after,
  .fold-marker:after {
    color: #e87b00;
  }

  .invisible {
    color: #555;
  }

  .selection .region {
    background-color: #e1e1e1;
  }

  .bracket-matcher .region {
    background-color: #C9C9C9;
    opacity: .7;
    border-bottom: 0 none;
  }

  &.is-focused {
    .cursor {
      border-color: @syntax-cursor-color;
    }

    .selection .region {
      background-color: @syntax-selection-color;
    }

    .line-number.cursor-line-no-selection,
    .line.cursor-line {
      background-color: @syntax-gutter-background-color-selected;
    }
  }
}