* {
    box-sizing: border-box;
}

body {
    margin: 0;
    background-size: cover;
    background-repeat: no-repeat;
    height: 100%;
}

.navbar {
    position: auto;
    overflow: hidden;
    background-color: #333;
    font-family: Arial, Helvetica, sans-serif;
    z-index: 1;
}

.navbar a {
    float: left;
    font-size: 16px;
    color: white;
    text-align: center;
    padding: 14px 16px;
    text-decoration: none;
    width: 16.66%
}


/* The subnavigation menu */

.subnav {
    float: left;
    overflow: hidden;
}


/* Subnav button */

.subnav .subnavbtn {
    font-size: 16px;
    border: none;
    outline: none;
    color: white;
    padding: 14px 16px;
    background-color: inherit;
    font-family: inherit;
    margin: 0;
}


/* Add a red background color to navigation links on hover */

.navbar a:hover,
.subnav:hover .subnavbtn {
    background-color: red;
}


/* Style the subnav content - positioned absolute */

.subnav-content {
    display: none;
    position: absolute;
    left: 0;
    background-color: red;
    width: 100%;
    z-index: 1;
}


/* Style the subnav links */

.subnav-content a {
    float: left;
    color: white;
    text-decoration: none;
}


/* Add a grey background color on hover */

.subnav-content a:hover {
    background-color: #eee;
    color: black;
}


/* When you move the mouse over the subnav container, open the subnav content */

.subnav:hover .subnav-content {
    display: block;
}

.sticky {
    position: fixed;
    top: 0;
    width: 100%;
}

.sticky+.content {
    padding-top: 30px;
}


/* The Overlay (background) */

.overlay {
    /* Height & width depends on how you want to reveal the overlay (see JS below) */
    height: 100%;
    width: 0;
    position: fixed;
    /* Stay in place */
    z-index: 1;
    /* Sit on top */
    left: 0;
    top: 0;
    background-color: rgb(0, 0, 0);
    /* Black fallback color */
    background-color: rgba(0, 0, 0, 0.9);
    /* Black w/opacity */
    overflow-x: hidden;
    /* Disable horizontal scroll */
    transition: 0.5s;
    /* 0.5 second transition effect to slide in or slide down the overlay (height or width, depending on reveal) */
}


/* Position the content inside the overlay */

.overlay-content {
    position: relative;
    top: 25%;
    /* 25% from the top */
    width: 100%;
    /* 100% width */
    text-align: center;
    /* Centered text/links */
    margin-top: 30px;
    /* 30px top margin to avoid conflict with the close button on smaller screens */
}


/* The navigation links inside the overlay */

.overlay a {
    padding: 8px;
    text-decoration: none;
    font-size: 36px;
    color: #818181;
    display: block;
    /* Display block instead of inline */
    transition: 0.3s;
    /* Transition effects on hover (color) */
}


/* When you mouse over the navigation links, change their color */

.overlay a:hover,
.overlay a:focus {
    color: #f1f1f1;
}


/* Position the close button (top right corner) */

.overlay .closebtn {
    position: absolute;
    top: 20px;
    right: 45px;
    font-size: 30px;
}

header {
    position: sticky;
    top: 0;
    height: calc(4.0em + 1px);
}


/* When the height of the screen is less than 450 pixels, change the font-size of the links and position the close button again, so they don't overlap */

@media screen and (max-height: 450px) {
    .overlay a {
        font-size: 20px
    }
    .overlay .closebtn {
        font-size: 40px;
        top: 15px;
        right: 35px;
    }
}