atom/packages/base16-tomorrow-light-theme/styles/editor.less

// Editor styles (background, gutter, guides)

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

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

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

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

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

    .line-number {
      padding: 0 0.25em 0 0.5em;
      -webkit-font-smoothing: antialiased;
      &.cursor-line {
        background-color: @syntax-gutter-background-color-selected;
        color: @syntax-gutter-text-color-selected;
      }

      &.cursor-line-no-selection {
        color: @syntax-gutter-text-color-selected;
      }
    }
  }

  .gutter .line-number.folded,
  .gutter .line-number:after,
  .fold-marker:after {
    color: @syntax-result-marker-color;
  }

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

  .cursor {
    color: @syntax-cursor-color;
  }

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

  .bracket-matcher .region {
    border-color: @syntax-result-marker-color;
  }
}