Simple Sass buttons

http://nadeemkhedr.wordpress.com/2014/02/22/why-sass-is-awesome-make-an-elegant-button-with-only-one-color-to-generate/

HTML

<div>
    <a class='my-btn'>My Button</a>
    <a class='my-btn disabled'>My Button</a>
</div>
<div>
    <a class='my-btn my-btn-primary'>My Button</a>
    <a class='my-btn my-btn-primary disabled'>My Button</a>
</div>
<div>
    <a class='my-btn my-btn-grey'>My Button</a>
    <a class='my-btn my-btn-grey disabled'>My Button</a>
</div>
<div>
    <a class='my-btn my-btn-danger'>My Button</a>
    <a class='my-btn my-btn-danger disabled'>My Button</a>
</div>

SCSS

div {
    margin-bottom: 20px;
}

/* Colors */
$btn-danger: #DA4F49;
$btn-default: #f96b2d;
$btn-primary: #3196cb;
$btn-grey: #999;
$btn-grey-hover: #777;
$btn-color: white;

/* Mixins */
@mixin btn-theme($btn-color) {
  background: transparent;
  border-color: darken($btn-color, 10%);
}
@mixin btn-theme-hover($btn-color, $hover-color: "") {
  @if $hover-color == "" {
    $hover-color: saturate($btn-color, 10%);
    $hover-color: darken($hover-color, 10%)
  }
  background: $hover-color;
  border-color: darken($btn-color, 20%);
}
@mixin btn-theme-disabled($btn-color) {
  background: lighten($btn-color, 20%);
  border-color: lighten($btn-color, 10%);
}

/* Primary button class with default color (orange) */
.my-btn {
  margin-bottom: 0;
  font-size: 14px;
  line-height: 20px;
  text-align: center;
  vertical-align: middle;
  cursor: pointer;
  padding: 5px 12px;
  border-radius: none;
  display: inline-block;
  border:1px solid;

  color: $btn-color;
  @include btn-theme($btn-default);
}
.my-btn:hover {
  color: $btn-color;
  text-decoration: none; 
  @include btn-theme-hover($btn-default);
 }
.my-btn.disabled, .my-btn.disabled:hover {
  -webkit-user-select: none;
  pointer-events: none;
  cursor: not-allowed;
  opacity: .65;
  @include btn-theme-disabled($btn-default);
}


/* Different versions of the button (extending) */
.my-btn.my-btn-primary {
  @include btn-theme($btn-primary);
}
.my-btn.my-btn-primary:hover {
  @include btn-theme-hover($btn-primary);
}
.my-btn.my-btn-primary.disabled, .my-btn.my-btn-primary.disabled:hover {
  @include btn-theme-disabled($btn-primary);
}

.my-btn.my-btn-grey {
  @include btn-theme($btn-grey);
}
.my-btn.my-btn-grey:hover {
  @include btn-theme-hover($btn-grey, $btn-grey-hover);
}
.my-btn.my-btn-grey.disabled, .my-btn.my-btn-grey.disabled:hover {
  @include btn-theme-disabled($btn-grey);
}

.my-btn.my-btn-danger {
  @include btn-theme($btn-danger)
}
.my-btn.my-btn-danger:hover {
  @include...