style.css

* {
    box-sizing: border-box;
}

body {
    margin: 0px;
    background-color: #000112;
    font-family: Arial, Helvetica, sans-serif;
}

.nav {
    height: auto;
    width: 100%;
    position: relative;
}

.nav>.nav-header {
    display: inline;
}

.nav>.nav-header>.nav-title {
    display: inline-block;
    font-size: 30px;
    color: #fff;
    margin: 12px 28px;
    font-weight: 900;
}

.nav>.nav-btn {
    display: none;
}

.nav>.nav-links {
    display: inline;
    float: right;
    font-size: 18px;
    margin-right: 40px;
}

.nav>.nav-links>a {
    display: inline-block;
    padding: 7px 10px;
    margin: 16px 15px;
    text-decoration: none;
    color: #efefef;
    transition: 200ms linear;
}

.nav>.nav-links>a:hover {
    background-color: #fff;
    color: #111;
    border-radius: 9px;
}

.nav>#nav-check {
    display: none;
}

@media (max-width:600px) {
    .nav>.nav-btn {
        display: inline-block;
        position: absolute;
        right: 0px;
        top: 0px;
    }
    .nav>.nav-btn>label {
        display: inline-block;
        width: 50px;
        height: 50px;
        padding: 13px;
    }
    .nav>.nav-btn>label:hover, .nav #nav-check:checked~.nav-btn>label {
        background-color: rgba(0, 0, 0, 0.3);
    }
    .nav>.nav-btn>label>span {
        display: block;
        width: 25px;
        height: 10px;
        border-top: 2px solid #eee;
    }
    .nav>.nav-links {
        position: absolute;
        display: block;
        width: 100%;
        background-color: #333;
        height: 0px;
        transition: all 0.3s ease-in;
        overflow-y: hidden;
        top: 50px;
        left: 0px;
    }
    .nav>.nav-links>a {
        display: block;
        width: 100%;
    }
    .nav>#nav-check:not(:checked)~.nav-links {
        height: 0px;
    }
    .nav>#nav-check:checked~.nav-links {
        height: calc(100vh - 50px);
        overflow: hidden;
        z-index: 100;
    }
    .nav>.nav-header>.nav-title {
        margin: 2px 20px;
    }
}

main {
    margin-top: 150px;
}

.hi {
    text-align: center;
    padding: 0 60px;
}

.title {
    color: #fff;
}

.description {
    color: #c7c7c7;
    border: 1px solid blue;
    border-radius: 9px;
    padding: 15px;
}