body{
    font-family: "Noto Serif JP", serif;
    font-optical-sizing: auto;
    font-weight: 500;
    font-style: normal;
    background: url(https://otonakukan.com/img/bg.jpg) fixed no-repeat top center;
    background-size: cover;
}

main{
    margin-top:5rem;
}

a:hover{
    opacity: 0.8;
    transition: 0.5s;
}

h1{
    width:min(1000px,90%);
    margin:0 auto;
}

h1 img{
    width:100%;
    height:auto;
}

.r18{
    width:min(75px,20%);
    height:auto;
    margin:2rem auto;
}

.r18 img{
    width:100%;
    height:auto;
}

nav{
    margin: 0 auto;
}

nav ul{
    display: flex;
    justify-content: center;
    flex-wrap: wrap;
}

nav li{
    width: min(350px, 80%);
    border: 1px solid #b5b5b5;
    padding: 1rem;
    text-align: center;
    margin: 1rem;
    box-shadow: 0 1px 10px rgba(0, 0, 0, 0.5);
}

nav li img{
    width:100%;
    height:auto;
}

.leave{
    margin:2rem auto;
    width: min(200px, 70%);
    display: block;
    border: 1px solid #b5b5b5;
    padding: 1rem;
    color:#555;
    text-align: center;
    font-size: 2rem;
    box-shadow: 0 1px 10px rgba(0, 0, 0, 0.5);
}

.leave span{
    font-size: 1rem;
    display: block;
}

footer{
    text-align: center;
    padding:1rem 0;
}