Bowhead

What? Permalink ¶

Bowhead is a small SCSS framework on which to implement your design tokens, spitting out CSS Variables with optional fallbacks.

Why? Permalink ¶

Implementing a design system or even a series of simple design tokens can come with some unpredictable mental overhead. Bowhead aims to reduce that mental overhead by abstracting the specifics of design tokens into human-sensible formats and nomenclature.

This has a positive effect that ranges from giving the colours in your design system fun and memorable names, to the time and effort saved when communicating about these colours with collaborators without getting bogged down by details, because let’s be real: you don’t want or need to memorise the six-character hex value for all your colours, nor does anyone else! Now imagine that scenario when applied to multiple times more design tokens.

Installation Permalink ¶

Available on npm:

npm install @chrisburnell/bowhead --save-dev

You can also download it directly from GitHub:

https://github.com/chrisburnell/bowhead/archive/master.zip

Make sure the browser support for CSS Variables meets your needs:

CSS Data Types Permalink ¶

CSS data types define typical values (including keywords and units) accepted by CSS properties and functions.

CSS data types on MDN

An important first step to using Bowhead is to understand how it categorises CSS properties by the different CSS data types. By and large, this is done by looking at what the expected values for a given property are:

selector {
	background-color: #b22222;
	color: #3cb371;
	outline-color: #d2b48c;

	padding: 0.5rem;
	margin: 2rem;

	display: flex;
	align-items: flex-start;
	justify-content: flex-end;
}

If we take the above snippet as an example, we can quickly identify two types of values present: colors and sizes. Colors typically stand out quite easily, and, historically, developers have done well to assign colors to variables to simplify their use throughout the codebase. Sizes, on the other hand, are rarely seen reflected as design tokens in CSS despite their frequent prescence in other forms of design tokens, e.g. the space around a logo or iconography is usually defined in a brand's guidelines.

Despite being presented in different formats, we can confidently say that background-color, color, and outline-color expect a color-type value, not only because color is in their names, but because we can interchange the values between the properties and they still make sense.

Sizes can take trickier forms to identify and categorise, and I recommend allowing for more sizes than you might expect at first and paring it back later. Getting everything categorised is the hard part; swapping tokens later becomes very trivial off the back of this up-front effort. Regardless, I attach any kind of distance-related value to a size, and, once again, we could interchange any of the values between padding, margin, border-width, or width and the CSS still makes sense.

Extrapolating from here across the vast variety of CSS properties and the data type of the values they expect, you end up with a map of most properties against value types:

color	size	alignment	…
background-color border-color outline-color color fill stroke …	width height padding margin border-width min-width max-width …	align-items justify-content …

With this knowledge under our belt, we can begin to define the design tokens for our particular project by fleshing out what values are available underneath each type:

color	size	alignment	…
#b22222 #3cb371 #d2b48c …	1em 20px 2px …	flex-start flex-end center …

Usage Permalink ¶

	Values	Description
$bowhead-variable-as-default (optional)	true (default) false	Decides whether or not use the CSS Variable or raw value when calling the @v function.
$bowhead-show-fallback (optional)	true (default) false	Decides whether or not to show a fallback value for the CSS Variable. Only works when $bowhead-variable-as-default is also true.
$bowhead-generate (optional)	true (default) false	Decides whether or not to generate CSS Variables for you.
$bowhead-property-map (optional)	See below.	Defines which data types each CSS property should map against.
$bowhead-type-map (optional)	See below.	Defines custom remapping to rename the built-in names for types.
$bowhead-tokens	See below.	Defines the design token values, categorised by data types.

№ 1. Variable As Default

$bowhead-variable-as-default: true;

body {
	color: v(color, brick);
}

body {
	color: var(--color-brick);
}

$bowhead-variable-as-default: false;

body {
	color: v(color, brick);
}

body {
	color: #b22222;
}

№ 2. Show Fallback Value

$bowhead-variable-as-default: true;
$bowhead-show-fallback: true;

body {
	@include v(color, desert);
}

body {
	color: #d2b48c;
	color: var(--color-desert);
}

$bowhead-variable-as-default: true;
$bowhead-show-fallback: false;

body {
	@include v(color, desert);
}

body {
	color: var(--color-desert);
}

When $bowhead-variable-as-default is false, $bowhead-show-fallback has no effect.

$bowhead-variable-as-default: false;
$bowhead-show-fallback: true;

body {
	@include v(color, desert);
}

body {
	color: #d2b48c;
}

$bowhead-variable-as-default: false;
$bowhead-show-fallback: false;

body {
	@include v(color, desert);
}

body {
	color: #d2b48c;
}

№ 3. Generating CSS Variables

$bowhead-generate: true;

:root {
	--size-small: 0.5rem;
	--size-medium: 1rem;
	--size-large: 2rem;
	--color-brick: #b22222;
	--color-plankton: #3cb371;
	--color-desert: #d2b48c;
	--opacity-alpha: 0.8;
	--opacity-beta: 0.5;
	--opacity-gamma: 0.2;
	--z-index-below: -1;
	--z-index-root: 0;
	--z-index-default: 1;
	--z-index-above: 2;
}

$bowhead-generate: false;

Nothing is generated!

№ 4. Property Map (optional)

$bowhead-property-map is another map that contains mappings from CSS properties (padding-left, border-bottom-right-radius, etc.) to our defined design token types (size, color, etc.), i.e.

$bowhead-property-map: (
	width: size,
	min-width: size,
	max-width: size,
	height: size,
	min-height: size,
	max-height: size,
	...
)

If you wish, you can create new mappings or overwrite existing defaults by defining your own property map, e.g.

$bowhead-property-map: (
	vertical-align: alignments
);

Where alignments would be one of your design token types, e.g.

$bowhead-tokens: (
	alignments: (
		default: baseline,
		alternate: middle
	),
	...
);

Bowhead will merge new types in your defined map into its own defaults automatically! Any that you re-declare will overwrite what exists as a default from Bowhead.

№ 5. Type Map (optional)

$bowhead-type-map is a map that allows defining alternate names for the data types, e.g.

$bowhead-type-map: (
	size: measure,
	...
)

№ 6. Tokens

$bowhead-tokens expects an SCSS map of types of tokens. These types could be a size, color, opacity, z-index, etc.

$bowhead-tokens: (
	size: (
		small:  0.5rem,
		medium:   1rem,
		large:	2rem
	),
	color: (
		brick:	#b22222,
		plankton: #3cb371,
		desert:   #d2b48c
	),
	opacity: (
		alpha: 0.8,
		beta:  0.5,
		gamma: 0.2
	),
	z-index: (
		below:  -1,
		root:	0,
		default: 1,
		above:   2
	)
);

---

Then you’ll have to include Bowhead in your SCSS somehow. You could use Webpack or something like that, or if you’re using npm, the below code snippet should suffice.

Take note that you need to define any of your Bowhead variables ($bowhead-tokens, $bowhead-show-fallback, $bowhead-generate(, $bowhead-property-map)) before importing Bowhead into your SCSS!

$bowhead-tokens: (
	...
);
$bowhead-show-fallback: true;
$bowhead-generate: true;
$bowhead-property-map: (
	...
);

@import "node_modules/@chrisburnell/bowhead/bowhead";

Finally, you can use either Bowhead's @v function, @v mixin, both, or the CSS Variables it can spit out on their own. However you use it is totally up to you! 😄

.thing {
	@include v(background-color, desert);
	@include v(color, brick);
	border: v(size, small) solid v(color, plankton);
	padding: v(size, medium) v(size, large);
	@include v(z-index, above);
	opacity: var(--opacity-alpha);
	// 1. if you only want the raw value, this is not really recommended:
	text-decoration-color: map-get(map-get($bowhead-tokens, "color"), "brick");
	// 2. this does the same for you:
	text-decoration-color: v(color, brick, true);
	// 3. so does this, although it includes the CSS Variable too:
	@include v(text-decoration-color, brick, true);
}

will generate…

.thing {
	background-color: #d2b48c;
	background-color: var(--color-desert);
	color: #b22222;
	color: var(--color-brick);
	border: var(--size-small) solid var(--color-plankton);
	padding: var(--size-medium) var(--size-large);
	z-index: 2;
	z-index: var(--z-index-above);
	opacity: var(--opacity-alpha);
	/* 1 */
	text-decoration-color: #b22222;
	/* 2 */
	text-decoration-color: #b22222;
	/* 3 */
	text-decoration-color: #b22222;
	text-decoration-color: var(--color-brick);
}

Extras Permalink ¶

Need a negative value? Use calc():

.thing {
	margin-left: calc(#{v(size, medium)} * -1);
}

Combining values? Same idea:

.thing {
	margin-left: calc(#{v(size, medium)} + #{v(size, small)});
}

What about multiple values in a function? Make sure you're using the raw values from the v() function:

.thing {
	background-color: rgba(v(color, desert, true), v(opacity, alpha, true));
}

Read more Permalink ¶

• Variables for Both
• Deep Dive into Colour