A mobile-first grid for Pure. This pull request has more information on how to use it. Ping me if you run into issues. This is BETA! https://github.com/yui/pure/pull/146

mobile-first-grid.css

.pure-g {
    letter-spacing: -0.31em; /* Webkit: collapse white-space between units */
    *letter-spacing: normal; /* reset IE < 8 */
    *word-spacing: -0.43em; /* IE < 8: collapse white-space between units */
    text-rendering: optimizespeed; /* Webkit: fixes text-rendering: optimizeLegibility */

    /*
    Sets the font stack to fonts known to work properly with the above letter
    and word spacings. See: https://github.com/yui/pure/issues/41/

    The following font stack makes Pure Grids work on all known environments.

    * FreeSans: Ships with many Linux distros, including Ubuntu

    * Arimo: Ships with Chrome OS. Arimo has to be defined before Helvetica and
      Arial to get picked up by the browser, even though neither is available
      in Chrome OS.

    * Droid Sans: Ships with all versions of Android.

    * Helvetica, Arial, sans-serif: Common font stack on OS X and Windows.
    */
    font-family: FreeSans, Arimo, "Droid Sans", Helvetica, Arial, sans-serif;

    /*
    Use flexbox when possible to avoid `letter-spacing` side-effects.

    NOTE: Firefox (as of 25) does not currently support flex-wrap, so the
    `-moz-` prefix version is omitted.
    */

    display: -webkit-flex;
    -webkit-flex-flow: row wrap;

    /* IE10 uses display: flexbox */
    display: -ms-flexbox;
    -ms-flex-flow: row wrap;
}

/* Opera as of 12 on Windows needs word-spacing.
   The ".opera-only" selector is used to prevent actual prefocus styling
   and is not required in markup.
*/
.opera-only :-o-prefocus,
.pure-g {
    word-spacing: -0.43em;
}

/*
Resets the font family back to the OS/browser's default sans-serif font,
this the same font stack that Normalize.css sets for the `body`.
*/
.pure-g [class *= "pure-u"] {
    font-family: sans-serif;
}

.unit {
    display: inline-block;
    *display: inline; /* IE < 8: fake inline-block */
    zoom: 1;
    letter-spacing: normal;
    word-spacing: normal;
    vertical-align: top;
    text-rendering: auto;
    font-size: 1rem;
    *font-size: 14px;
}

.unit img {
    max-width: 100%;
    height: auto; /* preserves aspect ratio */
}


/*csslint duplicate-properties:false; */
.default-1 {
  width: 100%;
  *width: 99.969%; }

.default-1-2 {
  width: 50%;
  *width: 49.969%; }

.default-1-3 {
  width: 33.33%;
  *width: 33.299%; }

.default-2-3 {
  width: 66.67%;
  *width: 66.639%; }

.default-1-4 {
  width: 25%;
  *width: 24.969%; }

.default-3-4 {
  width: 75%;
  *width: 74.969%; }

.default-1-5 {
  width: 20%;
  *width: 19.969%; }

.default-2-5 {
  width: 40%;
  *width: 39.969%; }

.default-3-5 {
  width: 60%;
  *width: 59.969%; }

.default-4-5 {
  width: 80%;
  *width: 79.969%; }

.default-1-6 {
  width: 16.66%;
  *width: 16.629%; }

.default-5-6 {
  width: 83.33%;
  *width: 83.299%; }

.default-1-8 {
  width: 12.5%;
  *width: 12.469%; }

.default-3-8 {
  width: 37.5%;
  *width: 37.469%; }

.default-5-8 {
  width: 62.5%;
  *width: 62.469%; }

.default-7-8 {
  width: 87.5%;
  *width: 87.469%; }

.default-1-12 {
  width: 8.33%;
  *width: 8.299%; }

.default-5-12 {
  width: 41.67%;
  *width: 41.639%; }

.default-7-12 {
  width: 58.33%;
  *width: 58.299%; }

.default-11-12 {
  width: 91.67%;
  *width: 91.639%; }

.default-1-24 {
  width: 4.17%;
  *width: 4.139%; }

.default-5-24 {
  width: 20.83%;
  *width: 20.799%; }

.default-7-24 {
  width: 29.17%;
  *width: 29.139%; }

.default-11-24 {
  width: 45.83%;
  *width: 45.799%; }

.default-13-24 {
  width: 54.17%;
  *width: 54.139%; }

.default-17-24 {
  width: 70.83%;
  *width: 70.799%; }

.default-19-24 {
  width: 79.17%;
  *width: 79.139%; }

.default-23-24 {
  width: 95.83%;
  *width: 95.799%; }

/*csslint regex-selectors:false, unqualified-attributes:false*/
/*
 * Right after 480px, the tablet rules kick in,
 * forcing the elements to update to these widths,
 * as they take precedence over default-* rules.
 *
 * There is no upper-limit on the width set here. This
 * allows the user to not specify a desktop-* rule
 * unless they explicitly want something different
 * to happen.
*/
@media (min-width: 480px) {
  .tablet-1 {
    width: 100%; }

  .tablet-1-2 {
    width: 50%; }

  .tablet-1-3 {
    width: 33.33%; }

  .tablet-2-3 {
    width: 66.67%; }

  .tablet-1-4 {
    width: 25%; }

  .tablet-3-4 {
    width: 75%; }

  .tablet-1-5 {
    width: 20%; }

  .tablet-2-5 {
    width: 40%; }

  .tablet-3-5 {
    width: 60%; }

  .tablet-4-5 {
    width: 80%; }

  .tablet-1-6 {
    width: 16.66%; }

  .tablet-5-6 {
    width: 83.33%; }

  .tablet-1-8 {
    width: 12.5%; }

  .tablet-3-8 {
    width: 37.5%; }

  .tablet-5-8 {
    width: 62.5%; }

  .tablet-7-8 {
    width: 87.5%; }

  .tablet-1-12 {
    width: 8.33%; }

  .tablet-5-12 {
    width: 41.67%; }

  .tablet-7-12 {
    width: 58.33%; }

  .tablet-11-12 {
    width: 91.67%; }

  .tablet-1-24 {
    width: 4.17%; }

  .tablet-5-24 {
    width: 20.83%; }

  .tablet-7-24 {
    width: 29.17%; }

  .tablet-11-24 {
    width: 45.83%; }

  .tablet-13-24 {
    width: 54.17%; }

  .tablet-17-24 {
    width: 70.83%; }

  .tablet-19-24 {
    width: 79.17%; }

  .tablet-23-24 {
    width: 95.83%; } }
/*
 * Right after 980px, the desktop rules kick in,
 * forcing the elements to update to these widths,
 * as they take precedence over default-* rules.
*/
@media (min-width: 980px) {
  .desktop-1 {
    width: 100%; }

  .desktop-1-2 {
    width: 50%; }

  .desktop-1-3 {
    width: 33.33%; }

  .desktop-2-3 {
    width: 66.67%; }

  .desktop-1-4 {
    width: 25%; }

  .desktop-3-4 {
    width: 75%; }

  .desktop-1-5 {
    width: 20%; }

  .desktop-2-5 {
    width: 40%; }

  .desktop-3-5 {
    width: 60%; }

  .desktop-4-5 {
    width: 80%; }

  .desktop-1-6 {
    width: 16.66%; }

  .desktop-5-6 {
    width: 83.33%; }

  .desktop-1-8 {
    width: 12.5%; }

  .desktop-3-8 {
    width: 37.5%; }

  .desktop-5-8 {
    width: 62.5%; }

  .desktop-7-8 {
    width: 87.5%; }

  .desktop-1-12 {
    width: 8.33%; }

  .desktop-5-12 {
    width: 41.67%; }

  .desktop-7-12 {
    width: 58.33%; }

  .desktop-11-12 {
    width: 91.67%; }

  .desktop-1-24 {
    width: 4.17%; }

  .desktop-5-24 {
    width: 20.83%; }

  .desktop-7-24 {
    width: 29.17%; }

  .desktop-11-24 {
    width: 45.83%; }

  .desktop-13-24 {
    width: 54.17%; }

  .desktop-17-24 {
    width: 70.83%; }

  .desktop-19-24 {
    width: 79.17%; }

  .desktop-23-24 {
    width: 95.83%; } }
@media (max-width: 767px) {
  .pure-hidden-phone {
    display: none; }

  .pure-visible-desktop {
    display: none; } }
@media (min-width: 768px) and (max-width: 979px) {
  .pure-hidden-tablet {
    display: none; }

  .pure-visible-desktop {
    display: none; } }