How to mix one class with another sass?

Question

Sass

Hello everyone, is it possible in sass to add the class declared above to another class?
For example:
I declare a class: btn-black

.btn-black
    background-color: transparent
    border: 1px solid #000
    border-radius: 0
    font-size: 20px
    transition: background-color .25s ease, color .25s ease
    &:hover
        color: #fff
        background-color: #000

How to add it to btn class via sass?
Let's say:

.btn
   @import .btn-black

Is there a way to mix classes?