We have 3 variables for button shadow:

• $btn-box-shadow
• $btn-focus-box-shadow
• $btn-active-box-shadow

2 issues here:

1. If i set $btn-box-shadow value to "none", button mixin generates incorrect box-shadow for :focus/.focus states:

box-shadow: none, 0 0 0 3px rgba(244, 67, 54, 0.5);

Same for $btn-focus-box-shadow variable.
2. Seems like i can't remove 3px shadow in focus/active states as it's hardcoded in button mixin:

box-shadow: $btn-box-shadow, 0 0 0 3px rgba($border, .5);

Please make it optional.