* {
    box-sizing: border-box;
    /* 枠線や余白を含めたサイズ計算にする（必須） */
    margin: 0;
    padding: 0;
}

body {
    color: #333;
    font-family: "Helvetica Neue", Arial, "Hiragino Kaku Gothic ProN", "Hiragino Sans", MeiYo, sans-serif;
    background-color: #f8f8f8;
}

header {
    width: 100%;
    margin: 0 auto 40px;
    padding: 50px 0 50px;
}

main {
    width: 90%;
    margin: 0 auto;
}

h1 {
    font-size: 1.3rem;
    text-align: center;
}

h2 {
    font-size: 1.1rem;
    border-bottom: 1px solid #ddd;
    margin: 0 0 30px;
    padding: 0 0 10px;
}

h3 {
    font-size: 1rem;
    margin: 0 0 10px;
}

p.description {
    margin: 0 0 30px;
}

ul {
    line-height: 2.5rem;
    list-style-type: disc;
    padding: 0 2rem 0;
    margin: 0 0 40px;
}

li a {
    text-decoration: underline;
    color: #6f6f6f;
}

li a:hover {
    color: #a1a1a1;
}

a.back-to-top {
    width: 80px;
    display: block;
    text-align: center;
    text-decoration: none;
    padding: 10px;
    margin: 0 0 40px;
    color: #fff;
    background-color: #6f6f6f;
    border-radius: 10px;
}

a.back-to-top:hover {
    background-color: #a1a1a1;
}

p.copyright {
    margin: 0 0 20px;
    text-align: center;
    font-size: 0.7rem;
    color: #999;
}


@media (min-width: 601px) {
    header {
        width: 600px;
        margin: 0 auto 40px;
        padding: 50px 0 50px;
    }
    main {
    width: 600px;
    margin: 0 auto;
}
}