HTML

<a href="#" class="ghostButton-simple">Hover Me</a><a href="#" class="ghostButton-3d">
  <div class="front">Hover Me</div>
  <div class="back">Thanks!</div></a>

LESS CSS SCSS

@bg: #1abc9c;
@c: white;

// GHOST BUTTON MIXIN - SIMPLE
.ghostButton-simple(@c:@c,@bg:@bg,@b:3px,@h:70px,@t:.3s){
  @w: @h*3;
  @f: @h/3;
  @m: @h/10;
  
  display: inline-block;
	position: relative;
	color: @c;
	width: @w;
	height: @h;
	line-height: @h;
	font-size: @f;
	text-align: center;
	text-transform: uppercase;
	text-decoration: none;
	font-weight: bold;
	transition: @t;
  	
  &:after,
  &:before {
      content: "";
      position: absolute;
  }
  &:after {
		background-color: @c;
		top: 50%;
		left: 50%;
		width: 0;
		height: 0;
		transform: translate(-50%,-50%);
		transition: @t;
		opacity: 1;
  }
  &:before {
		top: -(@m+@b);
		left: -(@m+@b);
		bottom: -(@m+@b);
		right: -(@m+@b);
		border: @b solid @c;
  }
  &:hover {
		background-color: @c;
		color: @bg;
    
    &:after {
			width: @w+(@m+@b);
			height: @h+(@m+@b);
			opacity: 0;
    }
  }
}
// USE:
.ghostButton-simple {
	.ghostButton-simple();
}

// GHOST BUTTON MIXIN - 3D
.ghostButton-3d(@c:@c,@bg:@bg,@b:3px,@h:70px,@t:.3s) {
  @w: @h*3;
  @f: @h/3;
  @m: @h/10;

  position: relative;
  top: 0;
  left: 0;
  display: inline-block;
  width: @w;
  height: @h;
  transition: @t;
  perspective: 1000;
  transform-style: preserve-3d;

  &:before {
		content: "";
		position: absolute;
		top: -(@m+@b);
		left: -(@m+@b);
		bottom: -(@m+@b);
		right: -(@m+@b);
		border: @b solid @c;
		transition: @t;
		transform-style: preserve-3d;
  }

  .front, .back {
    position: absolute;
    backface-visibility: hidden;
    color: @c;
    width: @w;
    height: @h;
    line-height: @h;
    font-size: @f;
    text-align: center;
    text-transform: uppercase;
    text-decoration: none;
    font-weight: bold;
    transition: @t;
  }
  .front {
    z-index: 2;
  }
  .back {     
    transform: rotate3d(45, 45, 0, 180deg);
    background-color: @c;
    color: @bg;
  }
  &:hover  {
    transform: rotate3d(45, 45, 0, 180deg);
  }
  &:hover:before {
    transform: rotate3d(45, -45, 0, 180deg);
  }

}
// USE:
.ghostButton-3d {
	.ghostButton-3d();
}


// GENERAL STYLES
@import url(http://fonts.googleapis.com/css?family=Cabin:700);

body {
  padding: 3em;
  background-color: @bg;
  font-family: 'Cabin', sans-serif;
}
a {
  float: left;
  margin: 0 2em 2em 0;
}