Here is an example of a simple three-column class:

.three-col {
       -moz-column-count: 3;
       -moz-column-gap: 20px;
       -webkit-column-count: 3;
       -webkit-column-gap: 20px;
}

Of which you would apply to a block of text like so:

<p class="three-col">Pellentesque habitant morbi tristique senectus et netus et malesuada fames ac turpis egestas. Vestibulum tortor quam, feugiat vitae, ultricies eget, tempor sit amet, ante. Donec eu libero sit amet quam egestas semper. Aenean ultricies mi vitae est. Mauris placerat eleifend leo. Quisque sit amet est et sapien ullamcorper pharetra. Vestibulum erat wisi, condimentum sed, commodo vitae, ornare sit amet, wisi. Aenean fermentum, elit eget tincidunt condimentum, eros ipsum rutrum orci, sagittis tempus lacus enim ac dui. Donec non enim in turpis pulvinar facilisis. Ut felis. Praesent dapibus, neque id cursus faucibus, tortor neque egestas augue, eu vulputate magna eros eu erat. Aliquam erat volutpat. Nam dui mi, tincidunt quis, accumsan porttitor, facilisis luctus, metus</p>

Example

Pellentesque habitant morbi tristique senectus et netus et malesuada fames ac turpis egestas. Vestibulum tortor quam, feugiat vitae, ultricies eget, tempor sit amet, ante. Donec eu libero sit amet quam egestas semper. Aenean ultricies mi vitae est. Mauris placerat eleifend leo. Quisque sit amet est et sapien ullamcorper pharetra. Vestibulum erat wisi, condimentum sed, commodo vitae, ornare sit amet, wisi. Aenean fermentum, elit eget tincidunt condimentum, eros ipsum rutrum orci, sagittis tempus lacus enim ac dui. Donec non enim in turpis pulvinar facilisis. Ut felis. Praesent dapibus, neque id cursus faucibus, tortor neque egestas augue, eu vulputate magna eros eu erat. Aliquam erat volutpat. Nam dui mi, tincidunt quis, accumsan porttitor, facilisis luctus, metus

Note that the height of each column is auto-balanced, as per the spec.

Also note this demo and sample code is using moz and webkit vendor prefixes, should only work in Gecko (Firefox 1.5+, et al.) and Webkit (Safari 3+, Chrome, et al.) browsers. No native support in Internet Explorer or Opera yet that I know of.

All Related Properties

.three-col {
       -moz-column-count: 3;
       -moz-column-gap: 20px;
       -webkit-column-count: 3;
       -webkit-column-gap : 20px;
       -moz-column-rule-color:  #ccc;
       -moz-column-rule-style:  solid;
       -moz-column-rule-width:  1px;
       -webkit-column-rule-color:  #ccc;
       -webkit-column-rule-style: solid ;
       -webkit-column-rule-width:  1px;
}

You can also set the column-width (with prefixes) but it generally makes more sense to let it auto calculate that.

The rule ("rule", as in, a line) will split the gap down the middle. You can use the same values as you would a border.

Take care not to have your text blocks be so enormously tall that they are taller than a (fairly small) browser window, otherwise it's the same problem as text being wider than the browser window (scrolling back and forth to read = sucks). Also consider text-align: justify;

JavaScript Fallback

Is presented in this A List Apart article.

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Doing it with pseudo elements

Using pseudo elements for multiple borders has fairly deep browser support as it's CSS 2.1 (not 3).

The element needing multiple borders should have its own border and relative positioning.

#borders {
   position: relative;
   border: 5px solid #f00;
}

The secondary border is added with a pseudo element. It is set with absolute positioning and inset with top/left/bottom/right values. This will also have a border and is kept beneath the content (preserving, for example, selectability of text and clickability of links) by giving it a negative z-index value.

#borders:before {
   content: " ";
   position: absolute;
   z-index: -1;
   top: 5px;
   left: 5px;
   right: 5px;
   bottom: 5px;
   border: 5px solid #ffea00;
}

You can do a third border by using the :after pseudo class as well. Take special note that Firefox 3 (pre 3.6) screws this up by supporting :after and :before, but not allowing them to be absolutely positioned (so it looks weird).

Other Ways

Don't forget about the outline property. While it's a bit more limited than border (goes around entire element no matter what) it's an extra free border if that's what you need.

outline: 5px solid red;

If you are down with CSS3, you can use box-shadow (one of the deepest supported properties of CSS3) to get infinite (!) box shadows, by comma separating values.

box-shadow:
  0 0 0 10px hsl(0, 0%, 80%),
  0 0 0 15px hsl(0, 0%, 90%);

View Demo

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Browsers that support multiple backgrounds (WebKit from the very early days, Firefox 3+) use a syntax like this:

#box {
  background: 
    url(icon.png) top left no-repeat, 
    url(texture.jpg), 
    url(top-edge.png) top left repeat-y;
}

They are comma separated values and there can be as many as you want with different URL's, positioning, and repeat values. You can even combine WebKit gradients into the mix:

#box {
	background: 
		url(../images/arrow.png) 15px center no-repeat,
		-webkit-gradient(linear,left top,left bottom,color-stop(0, #010101),color-stop(1, #181818));
}

Old school IE on the Mac would display the first background in the list, but other browsers that don't support it fail hard and just display no background. This makes it a hard case for progressive enhancement. That is, unless you use a tool like Modernizr to detect support for it and write a fallback selector which only declares one background for browsers that don't support it.

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Web pages on iOS by default have a "momentum" style scrolling where a flick of the finger sends the web page scrolling and it keeps going until eventually slowing down and stopping as if friction is slowing it down. Like if you were to push a hockey puck across the ice or something. You might think that any element with scrolling would have this behavior as well, but it doesn't. You can add it back with a special property.

.module {
  width: 300px;
  height: 200px;

  overflow-y: scroll; /* has to be scroll, not auto */
  -webkit-overflow-scrolling: touch;
}

Check out this Pen!

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The rem font-size unit is similar to em, only instead of cascading it's always relative to the root (html) element (more information). This has pretty good modern browser support, it's just IE 8 and down we need to provide px fallbacks for.
Instead of repeating ourselves everywhere, we can use a LESS or SASS mixins to keep it clean. These mixins assumes:

This code also use "vairable" in CSS

html {
  font-size: 62.5%; /* Sets up the Base 10 stuff */
}

.font-size(@sizeValue) {
  @remValue: @sizeValue;
  @pxValue: (@sizeValue * 10);
  font-size: ~"@{pxValue}px"; 
  font-size: ~"@{remValue}rem";
}

@mixin font-size($sizeValue: 1.6) {
  font-size: ($sizeValue * 10) + px;
  font-size: $sizeValue + rem;
}

Usage

p {
  .font-size(13);
}

p {
  @include font-size(13);
}

@function strip-unit($num) {
  @return $num / ($num * 0 + 1);
}

@mixin rem-fallback($property, $values...) {
  $max: length($values);
  $pxValues: '';
  $remValues: '';

  @for $i from 1 through $max {
    $value: strip-unit(nth($values, $i));
    $pxValues: #{$pxValues + $value*16}px;

    @if $i < $max {
      $pxValues: #{$pxValues + " "};
    }
  } 

  @for $i from 1 through $max {
    $value: strip-unit(nth($values, $i));
    $remValues: #{$remValues + $value}rem;

    @if $i < $max {
      $remValues: #{$remValues + " "};
    }
  } 
  
  #{$property}: $pxValues; 
  #{$property}: $remValues; 
}

@include rem-fallback(margin, 10, 20, 30, 40);

body {
  margin: 160px 320px 480px 640px;
  margin: 10rem 20rem 30rem 40rem; 
}

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html, body, div, span, applet, object, iframe,
h1, h2, h3, h4, h5, h6, p, blockquote, pre,
a, abbr, acronym, address, big, cite, code,
del, dfn, em, font, img, ins, kbd, q, s, samp,
small, strike, strong, sub, sup, tt, var,
dl, dt, dd, ol, ul, li,
fieldset, form, label, legend,
table, caption, tbody, tfoot, thead, tr, th, td {
	margin: 0;
	padding: 0;
	border: 0;
	outline: 0;
	font-weight: inherit;
	font-style: inherit;
	font-size: 100%;
	font-family: inherit;
	vertical-align: baseline;
}
/* remember to define focus styles! */
:focus {
	outline: 0;
}
body {
	line-height: 1;
	color: black;
	background: white;
}
ol, ul {
	list-style: none;
}
/* tables still need 'cellspacing="0"' in the markup */
table {
	border-collapse: separate;
	border-spacing: 0;
}
caption, th, td {
	text-align: left;
	font-weight: normal;
}
blockquote:before, blockquote:after,
q:before, q:after {
	content: "";
}
blockquote, q {
	quotes: "" "";
}

Source: Reset Reloaded

Condensed version:

html,body,div,span,applet,object,iframe,a,abbr,acronym,address,big,cite,code,del,dfn,em,font,img,ins,kbd,q,s,samp,small,strike,strong,sub,sup,tt,var,dl,dt,dd,ol,ul,li,h1,h2,h3,h4,h5,h6,pre,form,fieldset,input,textarea,label,legend,p,blockquote,table,caption,tbody,tfoot,thead,tr,th,td{margin:0;padding:0;border:0;outline:0;font-weight:inherit;font-style:inherit;font-size:100%;font-family:inherit;vertical-align:baseline;}body{line-height:1;color:black;background:white;}:focus{outline:0;}table{border-collapse:collapse;border-spacing:0;}caption,th,td{text-align:left;font-weight:normal;}fieldset,img{border:0;}address,caption,cite,code,dfn,em,strong,th,var{font-style:normal;font-weight:normal;}ol,ul{list-style:none;}h1,h2,h3,h4,h5,h6{font-size:100%;font-weight:normal;}blockquote:before,blockquote:after,q:before,q:after{content:"";}blockquote,q{quotes:"" "";}abbr,acronym{border:0;}

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/* Smartphones (portrait and landscape) ----------- */
@media only screen 
and (min-device-width : 320px) 
and (max-device-width : 480px) {
/* Styles */
}

/* Smartphones (landscape) ----------- */
@media only screen 
and (min-width : 321px) {
/* Styles */
}

/* Smartphones (portrait) ----------- */
@media only screen 
and (max-width : 320px) {
/* Styles */
}

/* iPads (portrait and landscape) ----------- */
@media only screen 
and (min-device-width : 768px) 
and (max-device-width : 1024px) {
/* Styles */
}

/* iPads (landscape) ----------- */
@media only screen 
and (min-device-width : 768px) 
and (max-device-width : 1024px) 
and (orientation : landscape) {
/* Styles */
}

/* iPads (portrait) ----------- */
@media only screen 
and (min-device-width : 768px) 
and (max-device-width : 1024px) 
and (orientation : portrait) {
/* Styles */
}

/* Desktops and laptops ----------- */
@media only screen 
and (min-width : 1224px) {
/* Styles */
}

/* Large screens ----------- */
@media only screen 
and (min-width : 1824px) {
/* Styles */
}

/* iPhone 4 ----------- */
@media
only screen and (-webkit-min-device-pixel-ratio : 1.5),
only screen and (min-device-pixel-ratio : 1.5) {
/* Styles */
}

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