rfs

Powerful & easy-to-use responsive resizing engine.

RFS is a unit resizing engine which was initially developed to resize font sizes (hence its abbreviation for Responsive Font Sizes). Nowadays RFS is capable of rescaling basically every value for any css property with units, like margin, padding, border-radiusor even box-shadow.

The mechanism automatically calculates the appropriate valuesbased on the dimensions of the browser viewport. It's available in one of your favourite preprocessors or postprocessor: , , or .

RFS

Demos

Advantages

  • No need to rescale paddings or margins anymore.
  • Text won't be chopped off in smaller viewports when RFS is applied to font sizes.
  • RFS will prevent the font size from rescaling too small, so readability can be assured.
  • The font sizes of all text elements will always remain in relation with each other.

Fluid rescaling in action

The following example shows the effect of RFS on font sizes:

Installation

RFS can be installed using a package manager (recommended):

  • npm: npm install rfs
  • yarn: yarn add rfs
  • bower (deprecated): bower install rfs --save

Copy/paste (not recommended):

The source files can also be downloaded manually and used in a project. This method is not recommended because you lose the ability to easily and quickly manage and update RFS as a dependency.

Usage

Sass (.scsssyntax)

project/
├── node_modules/
│   └── rfs
│        └── ...
└── scss/
    └── main.scss

Input

// scss/main.scss
@import "../node_modules/rfs/scss";
.title {
  @include font-size(4rem);
  // The font-size mixin is a shorthand which calls
  // @include rfs(4rem, font-size);
  // Other shorthand mixins that are available are:
  // @include padding(4rem);
  // @include padding-top(4rem);
  // @include padding-right(4rem);
  // @include padding-bottom(4rem);
  // @include padding-left(4rem);
  // @include margin(4rem);
  // @include margin-top(4rem);
  // @include margin-right(4rem);
  // @include margin-bottom(4rem);
  // @include margin-left(4rem);
  // For properties which do not have a shorthand, the property can be passed:
  // @include rfs(4rem, border-radius);
  // Whenever a value contains a space, it should be escaped with `#{}`:
  // @include rfs(0 0 4rem red #{","} 0 0 5rem blue, box-shadow);
  // Custom properties (css variables):
  // @include rfs(4rem, --border-radius);
}

If you're using Webpack, you can simplify the @importusing the ~prefix:

@import "~rfs/scss";

Generated css

.title {
  font-size: calc(1.525rem + 3.3vw);
}
@media (min-width: 1200px) {
  .title {
    font-size: 4rem;
  }
}

!important usage

Input
.label {
  @include font-size(2.5rem !important);
}
Output
.label {
  font-size: calc(1.375rem + 1.5vw) !important;
}
@media (min-width: 1200px) {
  .label {
    font-size: 2.5rem !important;
  }
}

Sass (.sasssyntax)

project/
├── node_modules/
│   └── rfs
│        └── ...
└── sass/
    └── main.sass

Input

// scss/main.scss
@import "../node_modules/rfs/sass"
.title
  +font-size(4rem)
  // The font-size mixin is a shorthand which calls
  // +rfs(4rem, font-size)
  // Other shorthand mixins that are available are:
  // +padding(4rem)
  // +padding-top(4rem)
  // +padding-right(4rem)
  // +padding-bottom(4rem)
  // +padding-left(4rem)
  // +margin(4rem)
  // +margin-top(4rem)
  // +margin-right(4rem)
  // +margin-bottom(4rem)
  // +margin-left(4rem)
  // For properties which do not have a shorthand, the property can be passed:
  // +rfs(4rem, border-radius)
  // Whenever a value contains a space, it should be escaped with `#{}`:
  // +rfs(0 0 4rem red #{","} 0 0 5rem blue, box-shadow)
  // Custom properties (css variables):
  // +rfs(4rem, --border-radius)

If you're using Webpack, you can simplify the @importusing the ~prefix:

@import "~rfs/scss"

Generated css

.title {
  font-size: calc(1.525rem + 3.3vw);
}
@media (min-width: 1200px) {
  .title {
    font-size: 4rem;
  }
}

!important usage

Input
.label
  +font-size(2.5rem !important)

output

.label {
  font-size: calc(1.375rem + 1.5vw) !important;
}
@media (min-width: 1200px) {
  .label {
    font-size: 2.5rem !important;
  }
}

PostCSS

project/
├── postcss/
│   └── main.css
└── node_modules/
    └── rfs
         └── ...

Have a look at the to find examples on how your PostCSS setup can be configured.

// postcss/main.css
.title {
  font-size: rfs(4rem);
  // Or use it with any other property, for example
  // padding: rfs(4rem);
  // It's also possible to pass multiple values
  // padding: rfs(3rem 4rem);
  // or even
  // box-shadow: rfs(0 3px 4rem red);
  // or even comma seperated values
  // box-shadow: rfs(0 3px 4rem red, 3px 0 4rem blue);
  // To combine it with !important, use
  // box-shadow: rfs(0 3px 4rem red) !important;
  // Custom properties (css variables):
  // --border-radius: rfs(4rem);
}

Generated css

.title {
  font-size: calc(1.525rem + 3.3vw);
}
@media (min-width: 1200px) {
  .title {
    font-size: 4rem;
  }
}

Less

project/
├── less/
│   └── main.less
└── node_modules/
    └── rfs
         └── ...
// less/main.less
@import "../node_modules/rfs/less";
.title {
  .font-size(4rem);
  // The font-size mixin is a shorthand which calls
  // .rfs(4rem, font-size);
  // Other shorthand mixins that are available are:
  // .padding(4rem);
  // .padding-top(4rem);
  // .padding-right(4rem);
  // 'padding-bottom(4rem);
  // .padding-left(4rem);
  // .margin(4rem);
  // .margin-top(4rem);
  // .margin-right(4rem);
  // .margin-bottom(4rem);
  // .margin-left(4rem);
  // For properties which do not have a shorthand, the property can be passed as:
  // .rfs(4rem, border-radius);
  // Whenever a value contains a space, it should be escaped with a tilde(~):
  // .rfs(0 0 4rem red ~"," 0 0 5rem blue, box-shadow)
  // Custom properties (css variables):
  // .rfs(4rem, --border-radius)
}

If you're using Webpack, you can simplify the @importusing the ~prefix:

@import "~rfs/less"

Generated css

.title {
  font-size: calc(1.525rem + 3.3vw);
}
@media (min-width: 1200px) {
  .title {
    font-size: 4rem;
  }
}

!important usage

Less still has for , and !importantcan not be accepted as a parameter, so you 'll need to pass importantas a flag:

Input
.label {
  .font-size(2.5rem important);
}

output

.label {
  font-size: calc(1.375rem + 1.5vw) !important;
}
@media (min-width: 1200px) {
  .label {
    font-size: 2.5rem !important;
  }
}

Stylus

project/
├── node_modules/
│   └── rfs
│        └── ...
└── stylus/
    └── main.styl
// stylus/main.styl
@import "../node_modules/rfs/stylus";
.title
  rfs-font-size(64px)
  // The font-size mixin is a shorthand which calls
  // rfs(4rem, font-size)
  // Other shorthand mixins that are available are:
  // rfs-padding(4rem)
  // rfs-padding-top(4rem)
  // rfs-padding-right(4rem)
  // rfs-padding-bottom(4rem)
  // rfs-padding-left(4rem)
  // rfs-margin(4rem)
  // rfs-margin-top(4rem)
  // rfs-margin-right(4rem)
  // rfs-margin-bottom(4rem)
  // rfs-margin-left(4rem)
  // For properties which do not have a shorthand, the property can be passed as:
  // rfs(4rem, border-radius)
  // Whenever a value contains a space, it should be escaped with a backslash:
  // rfs(0 0 4rem red \, 0 0 5rem blue, box-shadow)
  // Custom properties (css variables):
  // rfs(4rem, --border-radius)

Note the font-sizemixin can not be used to set the font size. That is because a font-size()mixin would override the font-sizeproperty. See for more info.

If you're using Webpack, you can simplify the @importusing the ~prefix:

@import "~rfs/stylus"

Generated css

.title {
  font-size: calc(1.525rem + 3.3vw);
}
@media (min-width: 1200px) {
  .title {
    font-size: 4rem;
  }
}

!important usage

Input
.label
  rfs-font-size(2.5rem important)

output

.label {
  font-size: calc(1.375rem + 1.5vw) !important;
}
@media (min-width: 1200px) {
  .label {
    font-size: 2.5rem !important;
  }
}

Visualisation

If you wonder how the values are rescaled, wonder no more and stare at this graph which might clarify things a bit:

Each color represents another value being rescaled. For example:

.title {
  @include font-size(40px);
}

This is the green line. A font size of 40pxstays 40pxin viewports with a size larger than 1200px. Below 1200px, the font size is rescaled and at viewport of 360px, the font size is about 27px. Note that every font size is generated in a combination of remand vwunits, but they are mapped to pxin the graph to make it easier to understand.

Configuration

RFS works out of the box without any configuration tweaks, but if you feel the urge to go loco and fine tune the way values are rescaled, you can:

Base value (unit in pxor rem)

  • SCSS, Sass & Stylus: $rfs-base-value
  • Less: @rfs-base-value
  • PostCSS: baseValue

The option will prevent the value from becoming too small on smaller screens. If the font size which is passed to RFS is smaller than this value, no fluid rescaling will take place.

Default value: 1.25rem

Unit (pxor rem)

  • SCSS, Sass & Stylus: $rfs-unit
  • Less: @rfs-unit
  • PostCSS: unit

The output value will be rendered in this unit. Keep in mind configuring this value to pxwill disable the ability for users to change the the font size in their browser.

Default value: rem

Breakpoint (in px, emor rem)

  • SCSS, Sass & Stylus: $rfs-breakpoint
  • Less: @rfs-breakpoint
  • PostCSS: breakpoint

Above this breakpoint, the value will be equal to the value you passed to RFS; below the breakpoint, the value will dynamically scale.

Default value: 1200px

Breakpoint unit (px, emor rem)

  • SCSS, Sass & Stylus: $rfs-breakpoint-unit
  • Less: @rfs-breakpoint-unit
  • PostCSS: breakpointUnit

The width of the max width in the media query will be rendered in this unit.

Default value: px

Factor (number)

  • SCSS, Sass & Stylus: $rfs-factor
  • Less: @rfs-factor
  • PostCSS: factor

This value determines the strength of font size resizing. The higher the factor, the less difference there is between values on small screens. The lower the factor, the less influence RFS has, which results in bigger values for small screens. The factor must be greater than 1.

Default value: 10

Rem value (number)

  • SCSS, Sass & Stylus: $rfs-rem-value
  • Less: @rfs-rem-value
  • PostCSS: remValue

The value of 1remin px. The value of 1remis typically 16pxbut if the font size is changed for htmlthe value of 1remchanges. This variable can be used to change the default value but be careful with it because changing it could lead to unexpected behaviour, for example if additional CSS is loaded which expects 1remto be 16px.

Default value: 16

Two dimensional (boolean)

  • SCSS, Sass & Stylus: $rfs-two-dimensional
  • Less: @rfs-two-dimensional
  • PostCSS: twoDimensional

Enabling the two dimensional media queries will determine the value based on the smallest side of the screen with vmin. This prevents values from changing if the device toggles between portrait and landscape mode.

Default value: false

Class (boolean)

  • SCSS, Sass & Stylus: $rfs-class
  • Less: @rfs-class
  • PostCSS: class

RFS can be enabled or disabled with a class. There are 3 options:

  • falseNo extra classes are generated.
  • disableWhen the the disable classes are generated you can add the .disable-rfsclass to an element to disable responsive value rescaling for the element and its child elements.
  • enableRFS is disabled by default in this case. The .enable-rfsclass can be added to an element to enable responsive value rescaling for the element and its child elements.

Default value: false

Safari iframe resize bug fix (boolean)

  • SCSS, Sass & Stylus: $rfs-safari-iframe-resize-bug-fix
  • Less: @rfs-safari-iframe-resize-bug-fix
  • PostCSS: safariIframeResizeBugFix

Safari doesn't resize its values in an iframe if the iframe is resized. To fix this min-width: 0vwcan be added and that's what happens if this option is enabled. See .

Default value: false

Best practices

  • Don't set RFS on the htmlelement, because this influences the value of remand could lead to unexpected results.
  • Always set your line-heights relative (in emor unitless) to prevent interline issues with font sizes.

Browser support

RFS is supported by all browsers that support and .

Creator

Martijn Cuppens

Copyright and license

Code released under .

HomePage

Repository

https+


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