Is there a limit for CSS variable count?

.btn {
 border: solid 1px Black;
 color: Black;
}

.btn.btn-primary {
 border-color: Blue;
 color: Blue;
}

.btn {
 --btnColor: Black;
 border: solid 1px var(--btnColor);
 color: var(--btnColor);
}

.btn.btn-primary {
 --btnColor: Blue;
}