.top{
    color:rgb(255, 255, 255);
    width:100%;
    background-image:url(https://play-college.jp/data/images/books.png);
    background-size:cover;
    text-align:center;
    padding:110px 0px;
}
.mail-img{
    vertical-align:middle;
    margin-right:10px;
    filter:invert(100%);
}
main{
    text-align:center;
}
.message h2{
    padding-top:30px;
    margin-top:50px;
    border-top:3px solid gray;
    text-align:center;
}
.content{
    display:inline-block;
    margin:10px;
    width:200px;
}
.content h4{
    text-align:center;
    width:100%;
    padding:25px 0px;
    border:5px double gray;
}
.content h4:hover{
    border:5px dotted gray;
}
.content a{
    text-decoration:none; /* リンクの下線を消す */
    color:black;
}
.content img{
    width:100%;
    height:100%;
}
.message{
    text-align:center;
    margin:0px 3% 100px 3%;
}
.message a,.top a{
    display:inline-block;
    text-decoration:none; /* リンクの下線を消す */
    border-radius:20px; /* ボタンの角を丸くする */
    background-color:rgba(0, 0, 0, 0.5);
    padding:30px 0px;
    margin:1%;
    width:200px;
}
.message a{
    color:white;
}
.top a{
    color:white;
}
.message a:hover,.top a:hover{
    background-color:rgba(128, 128, 128, 0.5);
}