<button class="modal-open">Open modal box</button>
<div class="modal-box">
    <div class="modal-box-content">
        <ul>
            <li><a href="#">One</a></li>
            <li><a href="#">Two</a></li>
            <li><a href="#">Three</a></li>
            <li><a href="#">Four</a></li>
            <li><a href="#">Five</a></li>
        </ul>
    </div>
    <button class="modal-close"><span class="visuallyhidden">Close modal box</span></button>
</div>

$ease: cubic-bezier(0.165, 0.84, 0.44, 1);
$highlight-color: #505050;

@mixin absolute-center {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
}

body {
    font-family: sans-serif;
    background-color: #1d1f20;
}

.modal-open {
    padding: 10px 0;
    font-weight: 300;
    letter-spacing: 3px;
    text-transform: uppercase;
    color: #fff;
    border: 0;
    outline: none;
    background-color: transparent;
    @include absolute-center;
    &:before,
    &:after {
        content: "";
        position: absolute;
        top: 100%;
        left: 0;
        height: 2px;
        transition: width 400ms $ease;
    }
    &:before {
        width: 100%;
        background-color: lighten($highlight-color, 30%);
    }
    &:after {
        width: 0;
        background-color: $highlight-color;
    }
    &:hover:after {
        width: calc(100% + 1px);
    }
}

.modal-box {
    position: absolute;
    overflow: hidden;
    width: 0;
    height: 2px;
    color: #fff;
    background-color: $highlight-color;
    transition: width 400ms 400ms $ease, left 400ms 400ms $ease, height 400ms 0ms $ease, top 400ms 0ms $ease;
    &.is-open {
        transition: width 400ms 0ms $ease, left 400ms 0ms $ease, height 400ms 400ms $ease, top 400ms 400ms $ease;
        li {
            opacity: 1;
        }
        .modal-close {
            opacity: 1;
            transition: all 500ms 700ms;
        }
    }
    ul {
        position: absolute;
        top: 50%;
        left: 50%;
        margin: 0;
        padding: 30px;
        list-style-type: none;
        transform: translate(-50%, -50%);
    }
    li {
        position: relative;
        margin: 20px 0;
        text-align: center;
        opacity: 0;
        transition: all 200ms;
    }
    a {
        position: relative;
        font-weight: 300;
        text-decoration: none;
        letter-spacing: 3px;
        text-transform: uppercase;
        color: #fff;
        &:before,
        &:after {
            content: "";
            position: absolute;
            top: 100%;
            left: 0;
            height: 2px;
            transition: width 400ms $ease;
        }
        &:after {
            width: 0;
            background-color: #fff;
        }
        &:hover:after {
            width: 100%;
        }
    }
    @for $i from 1 through 5 {
        &.is-open li:nth-child(#{$i}) {
            transition: all 500ms 500ms + (75ms * $i);
        }
    }
}

.modal-close {
    position: absolute;
    top: 10px;
    right: 10px;
    width: 15px;
    height: 15px;
    padding: 0;
    border: 0;
    outline: none;
    opacity: 0;
    background-color: transparent;
    transform: rotate(-45deg);
    &:before,
    &:after {
        content: "";
        display: block;
        position: absolute;
        top: 50%;
        left: 0;
        width: 15px;
        height: 3px;
        background-color: #fff;
        transform: translate(-50%, -50%);
    }
    &:after {
        width: 3px;
        height: 15px;
    }
}

.visuallyhidden {
    position: absolute;
    overflow: hidden;
    clip: rect(0 0 0 0);
    width: 1px;
    height: 1px;
    margin: -1px;
    padding: 0;
    border: 0;
}

var $trigger = $('.modal-open');
var $close = $('.modal-close');
var $modal = $('.modal-box');

$(window).on('resize', function() {
    var top = $trigger.offset().top + $trigger.outerHeight();
    var left = $trigger.offset().left;
    var width = $trigger.outerWidth();
    $trigger.attr({
        'data-top': top,
        'data-left': left,
        'data-width': width
    });
    $modal.css({
        top: top,
        left: left
    });
}).trigger('resize');

$trigger.on('click', function() {
    $modal.css({
        top: 0,
        left: 0,
        width: '100%',
        height: '100%'
    }).addClass('is-open');
});

$close.on('click', function() {
    var top = $trigger.offset().top + $trigger.outerHeight();
    var left = $trigger.offset().left;
    $modal.css({
        top: top,
        left: left,
        width: 0,
        height: '2px'
    }).removeClass('is-open');
});