This gist makes Pure Menus easier to customize, and adds a new responsive menu that collapses. Check out this pull request for details: https://github.com/yui/pure/pull/142 This is BETA!

responsive-menu.css

/*!
Pure 0.3.0
Copyright 2013 Yahoo! Inc. All rights reserved.
Licensed under the BSD License.
https://github.com/yui/pure/blob/master/LICENSE.md
*/
/*csslint adjoining-classes: false, box-model:false*/
.pure-menu ul, .pure-menu li {
    position: relative;
}
.pure-menu ul {
    list-style: none;
    margin: 0;
    padding: 0;
}
.pure-menu li {
    padding: 0;
    margin: 0;
    height: 100%;
}
.pure-menu a,
.pure-menu .pure-menu-heading {
    display: block;
    line-height: 1.5em;
    padding: 5px 20px;
    text-decoration: none;
    white-space: nowrap;
}

.pure-menu.pure-menu-horizontal > .pure-menu-heading {
    display: inline-block;
    *display: inline;
    zoom: 1;
    margin: 0;
    vertical-align: middle;
}
.pure-menu-horizontal > ul {
    display: inline-block;
    *display: inline;
    zoom: 1;
    vertical-align: middle;
}

.pure-menu li a { padding: 5px 20px; }

.pure-menu-can-have-children > .pure-menu-label {
    padding-right: 30px;
}

/* FIXED MENU */
.pure-menu-fixed {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
}


/* HORIZONTAL MENU */
.pure-menu-horizontal {
    width: 100%;
    border-left: none;
    border-right: none;
}

/* Initial menus should be inline-block so that they are horizontal */
.pure-menu-horizontal li {
    display: inline-block;
    *display: inline;
    zoom: 1;
    vertical-align: middle;
}

/* Submenus should still be display: block; */
.pure-menu-horizontal li li {
    display: block;
}

/* Adjusting separator for vertical menus */
.pure-menu-horizontal .pure-menu-separator {
    height: 50%;
    width: 1px;
    margin: 0 7px;
}

/* Submenus should be horizontal separator again */
.pure-menu-horizontal li .pure-menu-separator {
    height: 1px;
    width: auto;
    margin: 7px 2px;
}

/* RESPONSIVE MENUS */
/* Hide the toggle button by default. It will show on small screen sizes */
.pure-menu-responsive .pure-menu-toggle {
    float: right;
    text-transform: uppercase;
    font-size: 80%;
    display: none;
}

/* If the menu is open, and the viewport is larger than 767px, we
   still want the toggle button to show.
*/
.pure-menu-responsive.pure-menu-active .pure-menu-toggle {
    display: block;
}

.pure-menu-responsive .pure-menu-toggle:after {
    content: "\25BE";
    float: right;
    /* These specific fonts have the Unicode char we need. */
    font-family: 'Lucida Grande', 'Lucida Sans Unicode', 'DejaVu Sans', sans-serif;
    margin-right: -15px;
    margin-top: -1px;
}

.pure-menu-responsive.pure-menu-active ul, .pure-menu-responsive.pure-menu-active li {
    display: block;
}

.pure-menu-responsive.pure-menu-active .pure-menu-separator {
    width: auto;
    height: 1px;
}

/*csslint adjoining-classes: false, duplicate-properties:false*/

/* MENUS STYLING */
/* Focus style for a dropdown menu-item when the parent has been opened */
.pure-menu {
    background: #fff; /* need this to make menus stand out from page background */
    border: 1px solid #eee;
}
.pure-menu a {
    color: #666;
}
/* Hover and focus styles */
.pure-menu li a:hover,
.pure-menu li a:focus {
    background: #dedede;
    *background: #dedede;
    background: rgba(0,0,0,0.15);
}

/* DISABLED STATES */
/* need the .pure-menu prefix so that people over-riding `a` don't over-ride pure-menu-disabled too */
.pure-menu .pure-menu-disabled a,
.pure-menu .pure-menu-disabled a:hover,
.pure-menu .pure-menu-disabled a:focus {
    color: #bababa;
    *color: #bababa;
    color: rgba(0,0,0, 0.5);
    background: transparent;
}


.pure-menu-heading {
    color: #565d64;
    text-transform: uppercase;
    font-size: 90%;
    margin-top: 0.5em;
    border-bottom: 1px solid #eee;
}

.pure-menu-horizontal .pure-menu-heading {
    border-bottom: none;
}

/* ACTIVE MENU ITEM */
.pure-menu .pure-menu-selected a {
    color: #000;
}

/* FIXED MENU */
.pure-menu-fixed {
    border: none;
    border-bottom: 1px solid #b7b7b7;
    *border-bottom: 1px solid #b7b7b7;
    border-bottom: 1px solid rgba(0,0,0,0.4);
}

/*csslint box-model:false*/
/*TODO: Remove this lint rule override after a refactor of this code.*/


.pure-paginator {

    /* `pure-g` Grid styles */
    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 */

    /* `pure-paginator` Specific styles */
    list-style: none;
    margin: 0;
    padding: 0;
}
.opera-only :-o-prefocus,
.pure-paginator {
    word-spacing: -0.43em;
}

/* `pure-u` Grid styles */
.pure-paginator li {
    display: inline-block;
    *display: inline; /* IE < 8: fake inline-block */
    zoom: 1;
    letter-spacing: normal;
    word-spacing: normal;
    vertical-align: top;
    text-rendering: auto;
}


.pure-paginator .pure-button {
    border-radius: 0;
    padding: 0.8em 1.4em;
    vertical-align: top;
    height: 1.1em;
}
.pure-paginator .pure-button:focus,
.pure-paginator .pure-button:active {
    outline-style: none;
}
.pure-paginator .prev,
.pure-paginator .next {
    color: #C0C1C3;
    text-shadow: 0 -1px 0 rgba(0,0,0, 0.45);
}
.pure-paginator .prev {
    border-radius: 2px 0 0 2px;
}
.pure-paginator .next {
    border-radius: 0 2px 2px 0;
}

/*adjoining-classes: false*/
@media (max-width: 767px) {
    .pure-menu-responsive .pure-menu-toggle {
        display: block;
    }
    .pure-menu-responsive ul {
        display: none;
    }
    .pure-menu-responsive.pure-menu.active ul {
        display: inline-block;
        *display: inline;
        zoom: 1;
        vertical-align: middle;
    }

}