html {
    box-sizing: border-box;
}

*,
*:before,
*:after {
    box-sizing: inherit;
}

html, body {
    width: 100%;
    height: 100%;
    margin: auto;
}

body {
    font-family: Helvetica, Arial, sans-serif;
    font-size: 16px;
    max-width: 800px;
    display: flex;
    flex-direction: column;
    align-items: center;
}

header {
    margin-top: 40px;
    display: flex;
    flex-direction: column;
    align-items: center;

}

nav {
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
    margin: 40px 0;

    a {
        display: block;
        margin: 0 20px;
        opacity: .8;
    }
}

a {
    text-decoration: none;
}

main {
    margin: 20px;
    opacity: .8;
}

footer {
    margin-top: 40px;
    opacity: .3;
}