button {
    font-size: 30px;
    text-align: center;
    
}

#but {text-align: center;}

h1 {
    text-align: center;
    font-size: 80px;
     font-weight: bold;
     font-family: sans-serif;
     color: gold;
     background-color: violet;
     margin: 20px
    
}

.yellow {background-color: gold;

}
.purple {background-color: violet;

}

.a {margin-right: auto;
    margin-left: auto;
    display: block;
    height: auto;
    width: 800px;
}

.b {margin-right: auto;
    margin-left: auto;
    display: block;
    height: auto;
    width: 800px;
}

.c {margin-right: auto;
    margin-left: auto;
    display: block;
    height: auto;
    width: 800px;

}