What is this?

GEL Sass Tools is a collection of Sass variables, functions and mixins which allows you to work with GEL units consistently within your Sass. It is also required by other GEL Foundations components.

Here is how you could use these tools in your Sass:

.my-component {
    margin-top: $gel-spacing-unit;

    @include mq($from: gel-bp-m) {
        margin-top: double($gel-spacing-unit);
    }
}

This would compile to:

.my-component {
    margin-top: 8px;
}

@media (min-width: 37.50em) {
    .my-component {
        margin-top: 16px;
    }
}

Installation

Install using NPM

$ npm install --save gel-sass-tools

// your-app/main.scss
@import 'node_modules/gel-sass-tools/sass-tools';
@import 'node_modules/sass-mq/mq'

Install manually

You can install this component manually by downloading the content of this Git repo into your project and use a Sass @import to include it in your project.

Note: you will manually need to manage the dependencies below, without these this component will fail to compile.

Dependencies

In order to use the component you will need the following components available:

• Sass MQ

Usage

Usage of the included tools is as follows:

Spacing units

The following spacing variables are made available:

• $gel-spacing-unit - baseline spacing unit - 8px
• $gel-alt-spacing-unit - alternative baseline spacing unit - 12px

Breakpoints

The following breakpoints are defined and added to the Sass MQ breakpoint list:

• gel-bp-xs - 240px
• gel-bp-s - 400px
• gel-bp-m - 600px
• gel-bp-l - 900px
• gel-bp-xl - 1008px
• gel-bp-xxl - 1280px

These can be called when using the mq mixin:

.my-component {
    ...

    @include mq($from: gel-bp-s) {
        ...
    }

    @include mq($from: gel-bp-m) {
        ...
    }

    @include mq($from: gel-bp-l) {
        ...
    }
}

Math functions

The following math functions are included:

• quarter($value)
• third($value)
• halve($value)
• double($value)
• triple($value)
• quadruple($value)

These functions can be used inline with any numerical CSS rule. E.g:

.my-component {
    margin-bottom: halve($gel-spacing-unit);
    padding-left: double($gel-spacing-unit);
    padding-right: double($gel-spacing-unit);
}

or functions can be nested within other Sass features such as mixins:

.my-component {
    @include toRem('margin-bottom', halve($gel-spacing-unit));
    @include toRem('padding-left', double($gel-spacing-unit));
    @include toRem('padding-right', double($gel-spacing-unit));
}

REM mixin

The rem tool can be used in two ways. Either by directly calling the toRem($value) function, which will convert the supplied value and return a rem unit. E.g:

.my-component {
    margin-bottom: toRem($gel-spacing-unit);
}

Beware that rem units are not universal supported. IE8 and below do not support rem so require a px fallback.

You can also use the @include toRem($value); mixin, which by default returns a px fallback to allow support for older browsers which don't support rem units. E.g:

Sass

.my-component {
    @include toRem('margin-bottom', 16px);
}

CSS

.my-component {
    margin-bottom: 16px;
    margin-bottom: 1rem;
}

Options

The following options can be defined before the tools partial is included to customise the functionality and output. By default the following options are all set to true:

• $gel-tools-rem-enable--function - enable/disable the rem conversion, if this option is disabled only px values will be returned
• $gel-tools-rem-enable--mixin - disable the mixin if you only want to output the px, this can be useful for IE8 stylesheets who don't need rem values
• $tel-tools-rem-enable--fallback - disable the automatic generation of a px fallback when the mixin in called, use this open if you want to remove all px values from your stylesheets

Right-to-Left (RTL)

Support for Right-to-Left language is offered via two methods to flip CSS styles: interpolated properties and the flip() function.

Interpolation should be used for any property which has a direction (e.g. padding-left, margin-right, border-right, left, etc), `flip()`` should be used for all other properties.

Which properties need to be flipped?

• background
• background-position
• border
• border-radius
• clear
• cursor
• direction
• float
• left/right
• margin
• padding
• text-align
• text-indent

Flip

Taking the following CSS as an example:

// Original Sass
.my-component {
    float: left;
}

For a RTL layout, float: left; should be flipped to float: right;. We can use the flip() function to accomplish this.

// Flipped Sass
.my-component {
    float: flip(left, right);
}

When Sass comes across the flip() function, it will check the value of the $rtl variable. If $rtl is false, the flip() function will take the first parameter. If $rtl is true, the flip() function will take the second parameter.

The Sass will compile out as follows:

// Compiled LTR style
.my-component {
    float: left;
}

// Compiled RTL style
.my-component {
    float: right;
}

Interpolation

Interpolation is used to adjust CSS properties which contain a direction within their name. For example padding-left would need to change to padding-right in a RTL context. Our interpolation technique works by changing the value of variables based on the value of the $rtl variable.

Taking the following CSS as an example:

// Original Sass
.my-component {
    padding-left: $gel-spacing-unit; // 8px
}

For a RTL layout, padding-left: 8px; should be flipped to padding-right: 8px;.

In order to flip this, we have to interpolate the style property:

// Flipped Sass
.my-component {
    #{$padding-left}: $gel-spacing-unit; // 8px
}

This will compile out to:

// Compiled LTR style
.my-component {
    padding-left: 8px;
}

// Compiled RTL style
.my-component {
    padding-right: 8px;
}

Best practices & Tips

• Don't flip everything! Only flip what needs to be flipped. This will help keep the CSS as clean and predictable as possible.
• Styles which are hiding elements by pushing them off the screen (e.g. text-align: -320px; or right: 5000%;) don't need to be flipped unless they are being transitioned or overridden.
• If left and right properties have the same values in the same selector, they don't need to be flipped (e.g. margin-left: 0; margin-right: 0;)

Credits

• Shaun Bent
• Al Jones

License

The MIT License (MIT)

Copyright 2016 British Broadcasting Corporation

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.