gtk_study/builder.css

button {
    background: none;
    background-color: goldenrod;
    border: solid 0.5px #2f2d2d;
    border-radius: 0;
    font-size: 22px;
    color: gold;
}

#ok_button {
    background-color: greenyellow;
}

.cancel-button-class {
    background-color: red;
}