style.css

body{
    overflow-x: hidden;
    margin: 0;
    padding: 0;
}
#title{
    font-size: 50px; 
    margin-left: 40%;
    text-align: center;
}
.bt{
    border-style: solid;
    border-color: #008000;
    background-color: green;
    border-radius: 5px;
    color: white;
    text-decoration: none;
    font-size: 20px;
}
#mainImg{
    margin-left: 30%; 
    margin-right: auto; 
    width: 500px; 
    height: 300px;
}
#sub{
    text-align: center;
    font-size: 30px;
}
#bt1{
    margin-left: 40%;
}
#bt2{
    margin-left: 20px;
}

@media only screen and (max-width: 600px) {
    #title{
        font-size: 40px;
        margin-left: 0;
        margin-top: 20px;
    }
    #mainImg{
        width: 100%;
        height: auto;
        margin-left: 0;
        margin-top: 20px;
    }
    #sub{
        font-size: 20px;
    }
    #bt1{
        position: absolute;
        bottom: 20%;
        left: 30%;
        margin-left: 0;
    }
    #bt2{
        position: absolute;
        bottom: 10%;
        left: 35%;
        margin-left: 0;
    }
    
  }