referencing in less imports

.less

@import (less) "pure/base.css";

@import (reference,less) 'pure/grids.css';
@import (reference,less) 'pure/grids-responsive.css';
@import (reference,less) 'pure/buttons.css';
@import (reference,less) 'pure/menus.css';
@import (reference,less) 'pure/forms.css';
@import (reference,less) 'pure/tables.css';

//@import 'theme/global.less';
//@import 'theme/grids.less';
//@import 'theme/menus.less';

//global.less

html, button, input, select, textarea,
.pure-g [class *= "pure-u"] {
    font-family: 'Arimo', sans-serif;
}

body {
    line-height: 1.6;
    font-size: 1.125em;
}

h1, h2, h3, h4, h5, h6 {
    font-weight: normal;
    color: rgb(75, 75, 75);
}
h1 {
    font-size: 3em;
}
h2 {
    font-size: 1.5em;
}
h3 {
    font-size: 1.25em;
}
h4 {
    font-size: 1.125em;
}

blockquote {
    font-family: "Georgia", serif;
    color: #666;
    font-style: italic;
    line-height: 1.8;
    border-left: 5px solid #ddd;
    padding-left: 1.5em;
}

//grids.less
//General Layout
.site-content {
    padding-left: 2em;
    padding-right: 2em;
    margin-left: auto;
    margin-right: auto;
    max-width: 786px;
}
//Grid Rows
.mainmenu-container {
    &:extend(.pure-g all);
   // max-width: 980px;
   // margin: 0 auto;
}

//Grid Units
//nav
.brand, .main-menu {
    &:extend(.pure-u-1 all);
}
.brand {
    &:extend(.pure-u-md-1-3 all);
}
.main-menu {
    &:extend(.pure-u-md-2-3 all);
}

//menus.less
.mainmenu-container {
    margin-bottom: 1em;
    -webkit-font-smoothing: antialiased;
    height: 2.1em;
    overflow: hidden;
    -webkit-transition: height 0.5s;
    -moz-transition: height 0.5s;
    -ms-transition: height 0.5s;
    transition: height 0.5s;
    
    > div {
        > a {
            //the logo?
            &:extend(.pure-menu .pure-menu-heading all);
            &:extend(.pure-menu-horizontal .pure-menu-heading);
            &:extend(.pure-menu-horizontal > .pure-menu-heading all);
        }
        .menu {
            &:extend(.pure-menu);
            ul {
                &:extend(.pure-menu-list all);

                li {
                    &:extend(.pure-menu-item);
                }
                a {
                    &:extend(.pure-menu-link);
                }
                .current-menu-item a {
                    &:extend(.pure-menu-active > .pure-menu-link);
                }
            }
        }
        .menu-horizontal {
            &:extend(.pure-menu-horizontal all);
            ul {
                &:extend(.pure-menu-horizontal .pure-menu-list all);

                li {
                    &:extend(.pure-menu-horizontal .pure-menu-item);
                }
                a {
                    &:extend(.pure-menu-horizontal .pure-menu-link);
                }
                .current-menu-item a {
                    &:extend(.pure-menu-horizontal .pure-menu-active > .pure-menu-link);
                }
            }
        }
    }
    &.open {
        height: 14em;
    }

    .mainmenu-toggle {
        width: 34px;
        height: 34px;
        display: block;
        position: absolute;
        top: 0;
        right: 0;
        display: none;
    }

    .mainmenu-toggle .bar {
        background-color: #777;
        display: block;
        width: 20px;
        height: 2px;
        border-radius: 100px;
        position: absolute;
        top: 18px;
        right: 7px;
        -webkit-transition: all 0.5s;
        -moz-transition: all 0.5s;
        -ms-transition: all 0.5s;
        transition: all 0.5s;
    }

    .mainmenu-toggle .bar:first-child {
        -webkit-transform: translateY(-6px);
        -moz-transform: translateY(-6px);
        -ms-transform: translateY(-6px);
        transform: translateY(-6px);
    }

    .mainmenu-toggle.x .bar {
        -webkit-transform: rotate(45deg);
        -moz-transform: rotate(45deg);
        -ms-transform: rotate(45deg);
        transform: rotate(45deg);
    }

    .mainmenu-toggle.x .bar:first-child {
        -webkit-transform: rotate(-45deg);
        -moz-transform: rotate(-45deg);
        -ms-transform: rotate(-45deg);
        transform: rotate(-45deg);
    }

    @media (max-width: 47.999em) {

        .mainmenu-toggle {
            display: block;
        }

    }
}