header .btn_mypage_signin {
    display: inline-block;
    padding: 0 1.5vw;
    border: solid 1px #3A3A3A;
    border-radius: 100px;
    background-color: #F4F4F4;
    transition: all 0.3s;
}
header .btn_mypage_signin {
    background-color: #3A3A3A;
    color: #fff;
}
header .btn_mypage_signin:hover {
    color: #fff;
    border-color: #ACACAC;
    background-color: #ACACAC;
}

@media only screen and (min-width:1920px) {
    header .btn_mypage_signin {
        padding: 0 30px;
        border-radius: 100px;
    }
}

@media only screen and (max-width:768px) {
    header .btn_mypage_signin {
        display: block;
        padding: 10px 5px;
        border: none;
        border-radius: 0;
        border: 0;
    }
}