SCSS for responsive nav

main.scss

@import "bourbon/bourbon";
@import "colors";
@import url('https://fonts.googleapis.com/css?family=Inconsolata');
@import "grid";
@import "utils";

$parent_menu_items: 3;
$submenu_menu_items: 4;

html, body {
    margin: 0;
    padding: 0;
}

ul, li {
    list-style-type: none;
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

nav {
    > ul {
        height: 36px;
        @include clearfix;
        background-color: $light-blue;
    }

    > ul > li {
        font-size: 1.15em;
        @include size(medium-up) {
            display: inline-block;
            width: percentage((1/$parent_menu_items));
            a {
                border-right: 0.05em solid $white;
            }
        }
        &:last-child a {
            border-right: none;
        }
    }

    > ul.closed > li {
        display: none;
        @include size(medium-up) {
            display: block;
            float: left;
        }
    }
    
    a {
        font-family: 'Inconsolata', monospace;
        box-sizing: border-box;
        height: 36px;
        background-color: $light-blue;
        color: $white;
        border-bottom: 0.1em solid $white;
        text-decoration: none;
        display: block;
        padding: 6px 8px;
        text-align: center;
        &:hover {
            background-color: $dark-blue;
        }
    }
    
    // .submenu-parent {
    //     ul {
    //         display: none;
    //     }
    //     &:hover ul {
    //         display: block;
    //     }
    // }
    
    .submenu {
        display: none;
        @include size(medium) {
            position: absolute;
            left: 0;
            top: 35px;
            width: 100%;
            li {
                display: inline-block;
                margin-right: -5px;
                width: percentage((1/$submenu_menu_items));
                a {
                    border: 0;
                }
            }
        }
        a {
            border-bottom: none;
            
        }
        li:last-child {
            a {
                @include size(small) {
                    border-bottom: 0.05em solid $white;
                }
            }
        }
    }
}

#mobile-menu {
    display: block;
    @include size(medium-up) {
        display: none;
    }
}

#hamburger {
    $icon-width: 22px;
    float: left;
    margin: 2px -#{$icon-width} 2px 0;
    width: $icon-width;
    height: 16px;
    background-image: url('../img/Hamburger.png');
    background-size: cover;
}

ul.open #hamburger {
    $icon-width: 16px;
    margin: 2px -#{$icon-width} 2px 0;
    width: $icon-width;
    height: $icon-width;
    background-image: url('../img/X-Icon.png');
}