body{
    text-align: center;
}
.main{
    display: flex;
    justify-content: center;
}
.btn{
    height: 100px;
    width: 100px;
    border: 4px solid black;
    border-radius: 15px;
    margin: 10px;
}
.red{
    background-color: red;
}
.green{
    background-color: green;
}
.yellow{
    background-color: yellow;
}
.blue{
    background-color: blue;
}

.flash{
    background-color: white;
}