Classes can be combined, for example:
.btn .btn-lg .btn-outline-info .disabled
.btn .btn-sm
.btn
.btn .btn-lg
.btn .btn-primary
.btn .btn-secondary
.btn .btn-success
.btn .btn-info
.btn .btn-warning
.btn .btn-danger
.btn .btn-link
.btn .btn-block
.btn .btn-outline-primary
.btn .btn-outline-secondary
.btn .btn-outline-success
.btn .btn-outline-info
.btn .btn-outline-warning
.btn .btn-outline-danger
.btn .active
.btn .disabled