Bootstrap 4 customize button color

gistfile1.txt

2019 Update for Bootstrap 4

Now that Bootstrap 4 uses SASS, you can easily change the primary button color using the button-variant mixins:

.btn-danger {
    @include button-variant($red, darken($red, 7.5%), darken($red, 10%), lighten($red,5%), lighten($red, 10%), darken($red,30%));
}