Stylus PX to REM Mixin

By  on  

The REM unit is the hottest thing since Christina Ricci ... it's hot.  And it's especially hot when it comes to font size.  Rather than paraphrase a bunch of documentation as to why REM is important, I'd like to point you to Jonathan Snook's outstanding Font sizing with rem post, where he explains sizing with PX, EM, and how REM comes into the picture.  Here's how I implemented REM sizing within Stylus with a PX fallback!

The Stylus CSS

My method uses two mixins to accomplish the feat: one to set the base font-size and another to rem-ify the pixel unit:

set-font-size(value) {
    font-size: value; /* add PX (or original value) as backup */

    if (value is inherit) {
        /* do nothing, "inherit" has no unit */
    } else {
        font-size: remify(value);
    }
}

remify(value) { /* separate mixin, so it can be used elsewhere */
    u = unit(value);

    if (u is 'px') {
        return unit(value/16, 'rem');
    } else {
        return unit(value, u);
    }
}

The 16 within the remify unit represents the base font size, in pixels, that rems should be calculated by. The usage and output looks as follows:

.smaller {
	set-font-size(13px);
}

/*
	yields:

	.smaller {
		font-size: 13px;
		font-size: .8125rem;
	}

*/

Don't forget to set the base font size on the html element, usually 100%.  Also remember this mixin assumes a PX font is passed in, so if you aren't looking to use PX as backup, this isn't the solution for you.  If you do, however, there's no hurt in using these Stylus mixins!

Recent Features

  • By
    CSS @supports

    Feature detection via JavaScript is a client side best practice and for all the right reasons, but unfortunately that same functionality hasn't been available within CSS.  What we end up doing is repeating the same properties multiple times with each browser prefix.  Yuck.  Another thing we...

  • By
    9 Mind-Blowing Canvas Demos

    The <canvas> element has been a revelation for the visual experts among our ranks.  Canvas provides the means for incredible and efficient animations with the added bonus of no Flash; these developers can flash their awesome JavaScript skills instead.  Here are nine unbelievable canvas demos that...

Incredible Demos

  • By
    TextboxList for MooTools and jQuery by Guillermo Rauch

    I'll be honest with you: I still haven't figured out if I like my MooTools teammate Guillermo Rauch. He's got a lot stacked up against him. He's from Argentina so I get IM'ed about 10 times a day about how great Lionel...

  • By
    jQuery Chosen Plugin

    Without a doubt, my least favorite form element is the SELECT element.  The element is almost unstylable, looks different across platforms, has had inconsistent value access, and disaster that is the result of multiple=true is, well, a disaster.  Needless to say, whenever a developer goes...

Discussion

  1. You can also use this REM converter, which is really nice! https://offroadcode.com/prototypes/rem-calculator/

  2. I’ve been doing it px-ify style instead of remify!

    $default-font-size = 14px
    
    font-size(_size)
      if unit(_size) == 'rem'
        font-size: (_size * $default-font-size)px
      font-size: _size
    
    .bigger
      font-size(1.2rem)
    
  3. The first sentence in this post cracks me up every time. Oh and if anyone wants to remify multiple values you can just:

    remify() {
        remified = ();
    
        for arg in arguments {
            push(remified, unit(arg/16, 'rem'));
        }
        
        return remified;
    }
    

    so

    .foo {
        padding: remify(16px 32px 8px);
    }
    

    yields:

    .foo {
        padding: 1rem 2rem 0.5rem;
    }
    
  4. Mohamed Elkebir

    It’s best to let this code work with multi/mixed-values:

    pixify(property, sizes, base = 16)
      pixels = ()
      rems = ()
    
      for j, i in sizes
        if typeof(j) is 'unit'
          push(pixels, unit(j * base, 'px'))
          push(rems, unit(j, 'rem'))
        else
          push(pixels, j)
          push(rems, j)
    
      {property}: pixels
      {property}: rems
    

    Usage:

    pixify(border, 0.3 solid red)
    

Wrap your code in <pre class="{language}"></pre> tags, link to a GitHub gist, JSFiddle fiddle, or CodePen pen to embed!