Generated by SassMeister.com.

SassMeister-input-HTML.haml

%form.comment__form
  %button Submit
  
%form.product__form
  %button Submit

SassMeister-input.sass

// ----
// Sass (v3.3.0.rc.1)
// Compass (v0.13.alpha.10)
// ----

// MIXINS
@mixin btn-border($color)
  border: 1px solid darken($color, 10%)
  border-top-color: darken($color, 5%)
  border-bottom-width: 3px
  box-shadow: inset 0 1px 0 lighten($color, 15%)

@mixin mouse_interactions($color)
  &:hover
    background-color: lighten($color, 15%)
  
  &:active
    background-color: darken($color, 15%)
  
@mixin default_button($color)
  +btn-border($color)
  +mouse_interactions($color)
  
  background: $color
  border-radius: 3px

// BTN - BASE RESET
%btn
  border: none
  padding: 10px 20px
  +default_button(lightgray)

  &.btn--primary
    +default_button(blue)
    color: white
    
  &.btn--warning
    +default_button(orange)
    
  &.btn--danger
    +default_button(red)
    color: white
    
  &.btn--link
    +default_button(transparent)
    color: blue
    font-weight: bold
    
form
  @at-root .comment__#{&}
    button, .button
      @extend %btn.btn--primary
  @at-root .product__#{&}
    button, .button
      @extend %btn.btn--warning

SassMeister-output.css

.comment__form button, .comment__form .button {
  border: 1px solid #0000cc;
  border-top-color: #0000e6;
  border-bottom-width: 3px;
  box-shadow: inset 0 1px 0 #4d4dff;
  background: blue;
  border-radius: 3px;
  color: white;
}
.comment__form button:hover, .comment__form .button:hover {
  background-color: #4d4dff;
}
.comment__form button:active, .comment__form .button:active {
  background-color: #0000b3;
}
.product__form button, .product__form .button {
  border: 1px solid #cc8400;
  border-top-color: #e69500;
  border-bottom-width: 3px;
  box-shadow: inset 0 1px 0 #ffc04d;
  background: orange;
  border-radius: 3px;
}
.product__form button:hover, .product__form .button:hover {
  background-color: #ffc04d;
}
.product__form button:active, .product__form .button:active {
  background-color: #b37300;
}

SassMeister-rendered.html

<form class='comment__form'>
  <button>Submit</button>
</form>
<form class='product__form'>
  <button>Submit</button>
</form>