* {
    padding: 0;
    margin: 0;
    
}
.mainsection { 
    background-image: url(../images/mt07-3.jpg);
    background-repeat: no-repeat;
    background-attachment: fixed;
    background-size: cover;
    background-position: center;
    width: 100%;
    height: 100%;
    background-color: black;
}
.mydiv{
    height: 150px;
    width: 300px;
    background-color: black;
    border: 2px solid white;
    transition: 0.3s all ease-in-out;
    color: white;
     padding: 50px;
    margin: auto;
    font-size: calc(15px + (24 - 15) * ((100vw - 768px) / (1920 - 768)));
    
    
}
.mydiv:hover{
    background-color: red;
    border: 2px solid red;
}