* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    display: grid;
    grid-template-columns: 20% 80%;
    grid-template-areas:
        'header header'
        'sidebar videos'
        'footer footer';
    background-image: linear-gradient(to bottom, purple, blue);
    position: relative;
    font-family: 'Stack Sans Headline';
}

header {
    grid-area: header;
    display: flex;
    align-items: center;
    background-color: black;
    color: white;
    margin-bottom: 20px;
}

header img {
    border-radius: 50vh;
    padding: 1em;
}

#nav_list {
    grid-area: sidebar;
}

#nav_list ul {
    position: sticky;
    top: 20px;
}

#nav_list li {
    margin-bottom: 20px;
}

#nav_list a {
    display: block;
    background-color: cornsilk;
    color: black;
    padding: 8px 20px;
    border-radius: 8px;
    text-decoration: none;
    transition: all ease-in-out 200ms;
}

#nav_list a:hover {
    background-color: black;
    color: cornsilk;
}

section {
    max-width: 75%;
    margin: 0 auto;
}

main {
    grid-area: videos;
}

footer {
    grid-area: footer;
}

.videowrapper {
    position: relative;
    padding-bottom: 56.25%;
    /* 16:9 */
    padding-top: 25px;
    height: 0;
    margin: 0 auto;
    border: 6px ridge #808080;
}

.videowrapper iframe {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
}

.caption {
    margin-top: 10px;
    border-left: 10px solid cyan;
    color: white;
    padding-left: 10px;
    max-width: 75%;
}

article h4 {
    font-size: 200%;
    color: white;
}


#cornerBtn {
    display: none;
    position: fixed;
    bottom: 30px;
    left: 30px;
    z-index: 99;
    cursor: pointer;
}

footer {
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 150%;
    padding: 10px;
    color: white;
}

/* media query*/

@media (max-width: 767px) {
    #nav_list {
        display: none;
    }

    body {
        grid-template-columns: 1fr;
        grid-template-areas:
            'header'
            'videos'
            'footer';
    }

    section {
        max-width: 100%;
    }
}