foundation/stylus/foundation/components/button-groups.styl

You may also want to checkout:

//
// Button Group Variables
//
$include-html-button-classes ?= $include-html-classes !default;

// Sets the margin for the right side by default, and the left margin if right-to-left direction is used
$button-bar-margin-opposite ?= emCalc(10px);

//
// Button Group Mixins
//

// We use this to add styles for a button group container
button-group-container($styles=true, $float=false) {
  if $styles {
    list-style: none;
    margin: 0;
    clearfix();
  }
  if $float {
    float: $default-float;
    margin-{$opposite-direction}: $button-bar-margin-opposite;
    & div { overflow: hidden; }
  }
}

// We use this to control styles for button groups
button-group-style($radius=false, $even=false, $float=$default-float) {

  // We use this to control the flow, or remove those styles completely.
  if $float {
    margin: 0 0 0 -1px;
    float: $float;
    // Make sure the first child doesn't get the negative margin.
    &:first-child {
      margin-{$default-float}: 0;
    }
  }

  // We use these to control left and right radius on first/last buttons in the group.
  if $radius == true {
    &:first-child,
    &:first-child > a,
    &:first-child > button,
    &:first-child > .button {
      side-radius($default-float, $button-radius);
    }
    &:last-child,
    &:last-child > a,
    &:last-child > button,
    &:last-child > .button {
      side-radius($opposite-direction, $button-radius);
    }
  } else if $radius {
    &:first-child,
    &:first-child > a,
    &:first-child > button,
    &:first-child > .button {
      side-radius($default-float, $radius);
    }
    &:last-child,
    &:last-child > a,
    &:last-child > button,
    &:last-child > .button {
      side-radius($opposite-direction, $radius);
    }
  }

  // We use this to make the buttons even width across their container
  if $even {
    width: percent((100/$even));
    button, .button { width: 100%; }
  }

}

// Only include these CSS classes if $include-html-classes: true
if $include-html-button-classes != false {

  /* Button Groups */
  .button-group {
    button-group-container();

    &> * {
      button-group-style();
    }

    &.radius > * {
      button-group-style($radius:$button-radius, $float:null);
    }
    &.round > * {
      button-group-style($radius:$button-round, $float:null);
    }

    for $i in (2..8) {
      &.even-{$i} li {
        button-group-style($even:$i, $float:null);
      }
    }
  }

  .button-bar {
    clearfix();
    .button-group {
      button-group-container($styles:false,$float:true);
    }
  }

}