/* transition conf */
/* colors */
/* btn conf */
* {
  box-sizing: border-box;
  font-family: sans-serif;
}

body {
  background: #fcfcfc;
}

#btn-grp {
  max-width: 768px;
  margin: auto;
}

h1,
h2,
h3,
h4 {
  text-align: center;
  margin-bottom: 25px;
  color: #7f8c8d;
}

p {
  color: #7f8c8d;
}

.col-half {
  display: inline-block;
  width: 50%;
  margin-right: -3px;
  text-align: center;
}

.btn {
  margin: 25px auto;
  position: relative;
  font-size: 25px;
  color: #fff;
  padding: 20px;
  width: 200px;
  overflow: hidden;
  text-align: center;
  cursor: pointer;
  text-transform: uppercase;
}
.btn:nth-of-type(1) {
  background-color: #2ecc71;
}
.btn:nth-of-type(2) {
  background-color: #3498db;
}
.btn:nth-of-type(3) {
  background-color: #e74c3c;
}
.btn:nth-of-type(4) {
  background-color: #1abc9c;
}
.btn.left:after {
  left: 0;
}
.btn.right:after {
  right: 0;
}
.btn.wave:after {
  content: "";
  background: #fff;
  display: block;
  position: absolute;
  width: 200%;
  height: 200%;
  top: -5%;
  border-radius: 50px;
  margin-left: -30%;
  opacity: 0;
  transition: all 0.75s ease-in-out;
}
.btn.wave.right:after {
  content: "";
  background: #fff;
  display: block;
  position: absolute;
  width: 200%;
  height: 200%;
  top: -5%;
  border-radius: 50px;
  margin-right: -30%;
  opacity: 0;
  transition: all 0.75s ease-in-out;
}
.btn.wave:active:after {
  width: 0px;
  opacity: 1;
  transition: 0s;
}
.btn.stroke:after {
  content: "";
  background: #fff;
  display: block;
  position: absolute;
  width: 200%;
  height: 100%;
  top: 0;
  opacity: 0;
  transition: all 0.75s ease-in-out;
}
.btn.stroke:active:after {
  width: 0px;
  opacity: 1;
  transition: 0s;
}
.btn.half-stroke:after {
  content: "";
  background: #fff;
  display: block;
  position: absolute;
  width: 100%;
  height: 100%;
  top: 0;
  opacity: 0;
  transition: all 0.75s ease-in-out;
}
.btn.half-stroke:active:after {
  width: 0px;
  opacity: 1;
  transition: 0s;
}
.btn.bubble:after {
  content: "";
  background: #fff;
  position: absolute;
  width: 200px;
  height: 200px;
  left: 0;
  right: 0;
  top: 0;
  bottom: 0;
  opacity: 0;
  margin: auto;
  border-radius: 50%;
  transform: scale(1);
  transition: all 0.75s ease-in-out;
}
.btn.bubble:active:after {
  transform: scale(0);
  opacity: 1;
  transition: 0s;
}