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The atomic CSS compiler

Project description

blowdrycss is a rapid styling tool that compiles DRY CSS from encoded class selectors in your web project files.

Getting Started

Quick Start Docs

Full documentation

Version Changelog

See for full changelog.

1.0.0 – Enabled support for *.php extension and added integration tests. Incremented to 1.0.0 since the code is stable and working well.

1.0.1 – Enabled support for output file_name and extension customization. Created settings validation utility functions and unit tests. Custom output file examples: _blowdry.scss and custom.css. Added support for Python 3.6.

1.0.2 – Fixed file extension printing error. Now it uses the settings output_extension. Updated unit test.

Why the name blowdrycss?

Inspiration for the name came from the blow dryer. A blow dryer rapidly drys and styles hair.

Similarly, blowdrycss is used to rapidly style HTML and generate DRY CSS files using encoded class names.

Example Usage in HTML Tags:

Use the CSS level 1, 2.1, and 3 syntax that you already know.

<div class="text-align-center margin-top-30">
    <p class="font-size-25">
        The font-size is 25px. <span class="green">Green Text</span>

blowdrycss decodes the class names text-align-center, margin-top-30, font-size-25, and green; and generates the following atomic CSS in blowdry.css:

.text-align-center { text-align: center }
.margin-top-30 { margin-top: 30px }
.font-size-25 { font-size: 25px }
.green { color: green }

Advantages of blowdrycss

  1. Rapid Development: Less time spent writing CSS, and cleaning up unused style rules.

  2. DRY (Don’t Repeat Yourself): Reduces CSS file size by only defining properties once.

  3. Symbiotic:
    • Can be integrated with the current ecosystem of CSS compilers and frameworks. Compatible with SASS, SCSS, PostCSS, LESS, Foundation, Bootstrap.

    • Supports class selector discovery within HTML, JINJA, XHTML, .NET, Ruby ERB Templates, Javascript, and C#.

  4. Documented: Hands-on tutorial and sphinx documentation to get you up and running fast.

  5. Robust: Built for the real world in which deadlines and division of labor is not always taken into account. Can be used across all phases of a products lifecycle from prototype to production.

  6. Customizable: Features can be turned on and off inside of Examples include:
    • Watchdog file monitoring

    • Logging

    • Unit parsing

    • Color parsing

    • Font parsing

    • CSS Minification

    • Media query parsing.

  7. Atomic: Generates atomic CSS declarations.

  8. Standardized: HTML5 compatible. All W3C CSS Level 2.1, and Level 3 properties implemented. PEP8 Compliant.

  9. Tested: UnitTest Coverage

  10. Permissive: MIT license



  • tox 2.3.1+ (Multi-environment testing)

  • tox-travis 0.4+ (Allows tox to be used on Travis CI.)

  • coverage 4.0.2+ (Check test coverage)

  • coveralls 1.1+ (Used to report coverage when tox is run via Travis CI.)

  • sphinx 1.3.3+ (docs)

Pre-Requisite Knowledge

  • Basic HTML and CSS

  • Zero programming experience required.


This tool was created after seeing how many companies manage their CSS files. The following are some scenarios:

Scenario 1 - WET (Write Everything Twice) CSS

Inside a CSS file you find the following:

.header-1 { font-weight: bold; font-size: 12px; font-color: red; }
.header-2 { font-weight: bold; font-size: 16px; font-color: blue; }
.header-3 { font-weight: bold; font-size: 12px; font-color: green; }

The property font-weight: bold; appears three times, and font-size: 12px; appears twice. This is not DRY (Don’t Repeat Yourself).

Scenario 2 - Stale or Unused CSS

Inside a CSS file you find the following:

.banner-video {
    position: absolute;
    top: 48%;
    left: 50%;
    min-width: 100%;
    min-height: 100%;
    /*width: auto;*/
    /*max-height: 30.5em;*/
    z-index: -100;
    transform: translateX(-50%) translateY(-50%);
    background-color: rgba(0,0,0,1);
    background-size: contain;
    transition: 1s opacity;

Six months later the person who wrote this CSS is then asked to remove banner-video from the homepage. More often than not the front-end developer will remove the CSS class from the HTML file, but not from the CSS file. This leaves unused CSS lurking in the project.

Reasons include:

  • Forgetting to delete the rule from the CSS file.

  • Fear that the class is used somewhere else and that it might break the site.

  • Being too busy to search all of the files in their project for other potential use cases.

Now 326 bytes worth of stale CSS data lurks in the style files.

Scenario 3 - Modern CSS Pre-compiler:

CSS compilation with SASS/SCSS, PostCSS, or LESS is awesome, and makes writing lots of CSS rules easy. Tools like these allow auto-generation of hundreds of header rules like the ones above. If care is not taken this leverage can rapidly grow the CSS file.

SCSS Mixin example from a recent project:

@mixin text($font-color, $font-size, $font-family:"Open Sans", $line-height:inherit) {
    color: $font-color;
    font-size: $font-size;
    font-family: $font-family, $default-font-family;
    line-height: $line-height;

This mixin is called using @include as follows:

@include text($color-blue, rem-calc(14px), $default-font-family);

It turns out that @include text(...) is called 627 times in our SCSS. Most of these @include statements include at least one matching input parameter resulting in thousands of duplicate CSS properties.

Auto-generating font-size: 1rem; 500 times is now super easy with a pre-compiler and a for-loop. Some might say,

Well we minified it to save space.

Yes but,

Why did you write the same property 500 times in your main CSS file?

CSS File size does matter. For consideration:

  • Longer download times increase user bounce rates especially on mobile devices.

  • Data pollution on the Internet.

  • Increased likelihood of style bugs.

  • Increased time required to implement new changes and deprecate features.

What it is not

This tool is not designed to replace the need to hand-craft complex CSS property or rule declarations.

  • Custom CSS would need to be written for Multi-rule classes, Background images, url() values, multi-word fonts, and some shorthand properties.

The following is an example of something this tool in not intended to generate, and something that still needs to be written by hand.

.home-banner {
    background: url("") no-repeat;
    font-family: "Open Sans","Source Sans Pro",Arial;
    background-repeat: no-repeat;
    background-size: cover;
    min-height: 7rem;
    font-weight: bold;
    font-size: 3.5625rem;
    color: white;
    line-height: 3.6875rem;
    text-align: center;
    text-shadow: -2px 2px 4px rgba(0,0,0,0.5);

Valuable References

Blowdrycss Documentation

Github Repo

Slides presented at DessertPy

W3C Full CSS property table

Don’t Repeat Yourself

Download Python

cssutils 1.0.1+

watchdog 0.8.2+


The MIT license

How to Contribute

  • Open an Issue first and get community buy-in.

  • Write Code

  • Write Unit Tests (All tests must pass. 100% coverage preferred.)

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