Less mixin to calculate vertical rhythm styling for headings [in Bootstrap]. Don’t ask me how this works because I don’t remember and this made my brain hurt enough.

headings.less

.heading-line-height( @line-height ) when ( @line-height < 1 ) {
	line-height: unit(@line-height * 2, em);
}

.heading-line-height( @line-height ) when ( @line-height >= 1 ) {
	line-height: unit(@line-height, em);
}

.heading-rhythm ( @font-size-base, @font-size-increase ) {
	@heading-font-size: @font-size-base * @font-size-increase;
	@paragraph-line-height: @font-size-base * @line-height-base;
	@em-ratio: @paragraph-line-height / @heading-font-size;

	font-size:     unit( @font-size-increase, em );
	.heading-line-height( @em-ratio );
	margin-top:    unit( @em-ratio, em ) / 2;
	margin-bottom: unit( @em-ratio, em ) / 2;
}

.headings-rhythm( @font-size-base ) {

	h1, .h1, header a.brand {
		.heading-rhythm( @font-size-base, unit( @font-size-h1 ) )
	}

	h2, .h2 {
		.heading-rhythm( @font-size-base, unit( @font-size-h2 ) )
	}

	h3, .h3 {
		.heading-rhythm( @font-size-base, unit( @font-size-h3 ) )
	}

	h4, .h4 {
		.heading-rhythm( @font-size-base, unit( @font-size-h4 ) )
	}

	h5, .h5 {
		.heading-rhythm( @font-size-base, unit( @font-size-h5 ) )
	}

	h6, .h6 {
		.heading-rhythm( @font-size-base, unit( @font-size-h6 ) )
	}
}