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Generate CSS with Clojure
tag: v1.1.4

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Garden is a library for rendering CSS in Clojure and ClojureScript. Conceptually similar to Hiccup, it uses vectors to represent rules and maps to represent declarations. It is designed for stylesheet authors who are interested in what's possible when you trade a preprocessor for a programming language.

Table of contents


Add the following dependency to your project.clj file:

[garden "1.1.3"]


Garden syntax is very similar to Hiccup. If you're familiar with Hiccup you should feel right at home working with Garden. If not, don't sweat it! Garden's syntax is fairly simple.

From your project's root directory start up a new REPL and try the following:

user=> (require '[garden.core :refer [css]]))
user=> (css [:body {:font-size "16px"}])

First you'll notice the use of the css function. This function takes an optional map of compiler flags, any number of rules, and returns a string of compiled CSS. We'll start off by discussing rules then follow up with declarations and Garden's other utilities. Then we'll demonstrate the use of compiler flags.


As mentioned, vectors represent rules in CSS. The first n non-collection elements of a vector depict the rule's selector where n > 0. When n = 0 the rule is not rendered. To produce a rule which selects the <h1> and <h2> HTML elements for example, we simply begin a vector with [:h1 :h2].

user=> (css [:h1 :h2 {:font-weight "none"}])

To target child selectors nested vectors may be employed:

user=> (css [:h1 [:a {:text-decoration "none"}]])
"h1 a{text-decoration:none}"
user=> (css [:h1 :h2 [:a {:text-decoration "none"]])
"h1 a, h2 a{text-decoration:none}"

A slightly more complex example demonstrating nested vectors with multiple selectors:

user=> (css [:h1 :h2 {:font-weight "normal"}
             [:strong :b {:font-weight "bold"}]])
"h1,h2{font-weight:normal}h1 strong,h1 b,h2 strong,h2 b{font-weight:bold}"

Parent selector references

As in Sass, Garden also supports selectors prefixed with the & character allowing you to reference a parent selector.

user=> (css [:a
             {:font-weight 'normal
              :text-decoration 'none}
              {:font-weight 'bold
               :text-decoration 'underline}]])


Clojure maps represent CSS declarations where map keys and values represent CSS properties and values respectively. Garden's declaration syntax is a bit more involved than rules and understanding it is important to make the most of the library.


Declaration map keys should either be a string, keyword, or symbol:

user=> (css [:h1 {"font-weight" "normal"}])
user=> (css [:h1 {:font-weight "normal"}])
user=> (css [:h1 {'font-weight "normal"}])

Be aware Garden makes no attempt to validate your declarations and will not raise an error if other key types are used.

user=> (css [:h1 {30000 "nom-nom"}])


We've already seen strings used as declaration map values, but Garden also supports keywords, symbols, numbers, maps, vectors, and lists in addition.

Strings, keywords, symbols, and numbers

Strings, keywords, symbols, and numbers are rendered as literal CSS values:

user=> (css [:body {:font "16px sans-serif"}])
"body{font:16px sans-serif}"

Be warned, you must escape literal string values yourself:

user=> (css [:pre {:font-family "\"Liberation Mono\", Consolas, monospace"}])
"pre{font-family:\"Liberation Mono\", Consolas, monospace}"

In some cases it would be useful target several properties in a "group" of properties without having to type the same prefix several times. To do this with Garden we use maps. Maps as declaration values are used to denote a property suffix (IE. -family or -weight) and may be nested as deeply as you like.

Here are a few practical examples of where this technique might be handy:

user=> ;; Working with vendor prefixes:
user=> (css [
             {:-moz {:border-radius "3px"
                     :box-sizing "border-box"}}])
user=> ;; Creating DRY "mixins":
user=> (def reset-text-formatting
         {:font {:weight "normal" :style "normal" :variant "normal"}
          :text {:decoration "none"}})
user=> (css [:a reset-text-formatting])
user=> (defn partly-rounded
         ([r1] (partly-rounded r1 r1))
         ([r1 r2]
          {:border {:top-right-radius r1
                    :bottom-left-radius r2}}))
user=> (css [ (partly-rounded "3px")])
Vectors and lists

Finally we have vectors and lists which are handled in the same manor when used as a declaration value. The semantics of these values increment the level of complexity somewhat so be sure you understand their behavior before you use them. When you use a vector/list as a value you are asking Garden for a comma separated list.

user=> (css [:p {:font ["16px" "sans-serif"]}])

When you nest a vector/list you are asking for a space separated list.

user=> (css [:p {:font [["16px" 'Helvetica] 'Arial 'sans-serif]}])
"p{font:16px Helvetica,Arial,sans-serif}"


So far we've got all the core pieces to start building basic stylesheets. But it would be useful to have something for working with one of CSS's most fundamental data types: units!

Fortunately, Garden has built in support for working with all the major CSS units. This includes creation, conversion, and arithmetic. To start using units use/require the garden.units namespace.

user=> (require '[garden.units :as u :refer [px pt]])

For demonstration purposes we're only refering the px and pt units but Garden supports all of the usual suspects. Also we'll use the css macro to render the units as strings but note this is not necessary when authoring a stylesheet.

Unit creation is straightforward:

user=> (px 16)
#garden.types.CSSUnit{:unit :px, :magnitude 1}

To see the value as it would appear in CSS require the garden.repl namespace.

user=> (require 'garden.repl)
user=> (px 16)

Unit functions take a number n and construct a new garden.types.CSSUnit record with n as the magnitude. Unit functions also accept other units as values returning their conversion if possible. This makes working with unit values very flexible.

user=> (px (px 16))
user=> (px (pt 1))

Unit arithmetic is available via the - spoiler alert- unit arithmetic functions.

user=> (require '[garden.units :refer (px+ px* px- px-div)])
user=> (px+ 1 2 3 4 6)
user=> (px-div 2 4)
user=> (px* 2 2)

Since the arithmetic functions use the primary unit functions in their definitions, conversion occurs seamlessly (when possible):

user=> (px* 2 (pt 1))

You might be wondering, which units can be converted to another? This depends on the type of unit you are working with. The CSS spec outlines a few categories of units but only absolute (px, pt, pc, in, cm, and mm), angle (deg, grad, rad, turn), time (s, ms), and frequency (Hz, kHz) units may be freely converted and only between their respective groups. This means you cannot, for example, convert px to rad or Hz to cm. Doing so will raise an error.

In the future, some exceptions to this rule might apply for working with ems since it's technically possible to compute their contextual value.


What would a stylesheet be like with out color? No fun. That's what it would be like. And the person who's interested in writing a stylesheet in Clojure probably wants tools for working with color. Who wants to write a stylesheet where colors are strings that look like "#A55"? No one. That's who.

Since 0.1.0-beta5 Garden comes with a (mostly) complete set of functions for dealing with colors. If you've worked with Sass you'll be pleased to know many of the same color functions are available in Garden.

Garden's color functions are available in the garden.color namespace.

user=> (require '[garden.color :as color :refer [hsl rgb]])

Let's create a color to work with.

user> (def red (hsl 0 100 50))
user> red

We've defined red in terms of the HSL value for pure red with the hsl function (rgb is also available). When we evaluate the value of red at the REPL we notice it is displayed in the familiar hexadecimal format.

Let's apply some color functions to it. By the way, if you're using Emacs, try turning on rainbow-mode to see the colors highlighted.

;; Make dark red.
user> (color/darken red 25)
;; Make light red.
user> (color/lighten red 25)

But, wait! There's more!

;; Make an orange color...
user> (def orange (color/hsl 30 100 50))
;; ...and mix it with red.
user> (color/mix red orange)
;; Make a green color...
user> (def green (hsl 120 100 50))
;; ...and add it to red to get yellow.
user> (color/color+ red green)
;; Get a set of analogous colors.
user> (color/analogous red)
(#ff0000 #ff8000 #ffff00)

As with units, colors can be added, subtracted, divided and multiplied with color+, color-, color*, and color-div respectively. There are several other nice functions available for finding color complements, triads, tetrads, and more.


Now that we have a solid understanding of how units and colors operate, we can talk about Garden's generic arithmetic operators. While working with functions like px+, color+, etc. have their advantages, sometimes they can get in the way. To get around this you can use the operators in the garden.arithmetic namespace.

(ns user
  ;; Unless you want to see a bunch of warnings add this line.
  (:refer-clojure :exclude '[+ - * /])
  (:require '[garden.arithmetic :refer [+ - * /]]))

This will allow you to perform operations like this:

user> (+ 20 (color/hsl 0 0 0) 1 (color/rgb 255 0 0))
user> (- 20 (px 1) 5 (pt 5))

Media queries

Authoring stylesheets these days without media queries is somewhat like having prime rib without horseradish. Garden provides the at-media function available in the garden.stylesheet namespace.

user=> (require '[garden.stylesheet :refer [at-media]])
user=> (css (at-media {:screen true} [:h1 {:font-weight "bold"}]))
"@media screen{h1{font-weight:bold}}"
user=> (css
         (at-media {:min-width (px 768) :max-width (px 979)}
           [:container {:width (px 960)}])
"@media (max-width:979px) and (min-width:768px){container{width:960px}}"

Media queries may also be nested:

user=> (css [:a {:font-weight "normal"}
             [:&:hover {:color "red"}]
             (at-media {:screen true}
               [:&:hover {:color "pink"}])])

and will out put the equivalent CSS:

a {
  font-weight: normal;

a:hover {
  color: red;

@media screen {

  a:hover {
    color: pink;


To understand how media expressions are interpreted refer to this table:

Map Interpretation
{:screen true} screen
{:screen false} not screen
{:screen true :braille false} screen and not braille
{:screen :only} only screen
{:min-width (px 768) :max-width (px 959)} (min-width: 768px) and (max-width: 959)

Compiler flags

The css function optionally takes a map of compiler flags.

Output flags


Often you are interested in saving a fully expanded result of compilation for development and a compressed version for production. This is controlled by the :pretty-print? flag which may either be true or false. By default this flag is set to true.


(def styles
  [[:h1 {:font-weight "normal"}]
    [:a {:text-decoration "none"}]])

(css {:pretty-print? true} styles) results in the following output when compiled:

h1 {
  font-weight: normal;

a {
  text-decoration: none;

(css {:pretty-print? false} styles) results in the following output when compiled:


For Clojure generated stylesheets are compressed using the YUI Compressor which yeilds much better results when compared with the previous versions.

user=> (css {:pretty-print? false} [:body {:background "#ff0000"}])
user> (css {:pretty-print? false} [:div {:box-shadow [[(px 0) (px 0.5) (hsl 0 0 0)]]}])
"div{box-shadow:0 .5px #000}"

For ClojureScript compression mostly consists of whitespace elimination wherever possible.


Note: This is currently not available for ClojureScript, but support is planned.

To save a stylesheet to disk simply set the :output-to flag to the desired path.

user=> (css {:output-to "foo.css"} [:h1 {:font-weight "normal"}])
Wrote: foo.css
"h1 {\n  font-weight: normal;\n}"


Vendor prefixing can be a pain but Garden can help with that in some cases if you set the :vendors flag. The value is expeced to be a vector of prefixes (ie ["webkit" "moz" "o"]). By specifying this Garden will automatically prefix declarations tagged with the ^:prefix meta and @keyfames.


(require '[garden.def :refer [defrule defkeyframes]])

(defkeyframes pulse
   {:opacity 0}]

   {:opacity 1}])

(css {:vendors ["webkit"]
      :output-to "foo.css"}

  ;; Include our keyframes

   ;; Notice we don't need to quote pulse.
   ^:prefix {:animation [[pulse "2s" :infinite :alternate]]}])

will produce

@keyframes pulse {

  from {
    opacity: 0;

  to {
    opacity: 1;


@-webkit-keyframes pulse {

  from {
    opacity: 0;

  to {
    opacity: 1;


h1 {
  -webkit-animation: pulse 2s infinite alternate;
  animation: pulse 2s infinite alternate;


Listed by first commit:


If you're interested in automatically compiling your stylesheets be sure to check out the lein-garden plugin.


A big thank you goes out to @weavejester for creating Hiccup, @briancarper for creating gaka, and @paraseba for creating cssgen. I learned a lot from studying the source code of these libraries (and borrowed several ideas from them). Writing this library would have been significantly more difficult without the hard work of these individuals.

I'd also like to thank @jhardy for putting up with random questions and pushing me to keep working on this library.

Thanks to everyone in #clojure on IRC for answering my questions and being patient with me. If you're looking for an example of a great community, look no further.


Copyright © 2013 Joel Holdbrooks

Distributed under the Eclipse Public License, the same as Clojure.

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