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;
                    }