Full screen menu

<div class="container">
<!-- The close button -->
<button class="container__close">
...
</button>
<!-- The navigation menu -->
<ul>
...
</ul>
</div>
.container {
/* Full screen overlay */
height: 100%;
left: 0;
position: fixed;
top: 0;
width: 100%;
/* Center the content */
align-items: center;
display: flex;
justify-content: center;
}
.container__close {
/* Shown at top right corner */
position: absolute;
right: 16px;
top: 16px;
}