button.btn.first {
    margin: 0;
    width: 100%;
    height: 50px;
}

button.btn.third {
    margin: 30px auto 20px;
    width: 50%;
    height: 60px;
}

.btn {
    box-sizing: border-box;
    -webkit-appearance: none;
     -moz-appearance: none;
          appearance: none;
    background-color: transparent;
    border: 2px solid #000;
    border-radius: 0.6em;
    color: #3cd4c5;
    cursor: pointer;
    display: block;
    align-self: center;
    font-size: 1rem;
    font-weight: 400;
    line-height: 1;
    text-decoration: none;
    text-align: center;
    font-family: 'Montserrat', sans-serif;
    font-size: 26px;
}
.btn:hover, .btn:focus {
  color: #fff;
  outline: 0;
}

.first {
  transition: box-shadow 300ms ease-in-out, color 300ms ease-in-out;
}
.first:hover {
  box-shadow: 0 0 40px 40px #ef4c4d inset;
}

.second {
  border-radius: 3em;
  border-color: #1abc9c;
  color: #fff;
  background-image: linear-gradient(to right, rgba(26, 188, 156, 0.6), rgba(26, 188, 156, 0.6) 5%, #1abc9c 5%, #1abc9c 10%, rgba(26, 188, 156, 0.6) 10%, rgba(26, 188, 156, 0.6) 15%, #1abc9c 15%, #1abc9c 20%, rgba(26, 188, 156, 0.6) 20%, rgba(26, 188, 156, 0.6) 25%, #1abc9c 25%, #1abc9c 30%, rgba(26, 188, 156, 0.6) 30%, rgba(26, 188, 156, 0.6) 35%, #1abc9c 35%, #1abc9c 40%, rgba(26, 188, 156, 0.6) 40%, rgba(26, 188, 156, 0.6) 45%, #1abc9c 45%, #1abc9c 50%, rgba(26, 188, 156, 0.6) 50%, rgba(26, 188, 156, 0.6) 55%, #1abc9c 55%, #1abc9c 60%, rgba(26, 188, 156, 0.6) 60%, rgba(26, 188, 156, 0.6) 65%, #1abc9c 65%, #1abc9c 70%, rgba(26, 188, 156, 0.6) 70%, rgba(26, 188, 156, 0.6) 75%, #1abc9c 75%, #1abc9c 80%, rgba(26, 188, 156, 0.6) 80%, rgba(26, 188, 156, 0.6) 85%, #1abc9c 85%, #1abc9c 90%, rgba(26, 188, 156, 0.6) 90%, rgba(26, 188, 156, 0.6) 95%, #1abc9c 95%, #1abc9c 100%);
  background-position: 0 0;
  background-size: 100%;
  transition: background 300ms ease-in-out;
}
.second:hover {
  background-position: 100px;
}

.third {
  border-color: #3498db;
  color: #fff;
  box-shadow: 0 0 40px 40px #3498db inset, 0 0 0 0 #3498db;
  transition: all 150ms ease-in-out;
}
.third:hover {
  box-shadow: 0 0 10px 0 #3498db inset, 0 0 10px 4px #3498db;
}

.fourth {
  border-color: #f1c40f;
  color: #fff;
  background-image: linear-gradient(45deg, #f1c40f 50%, transparent 50%);
  background-position: 100%;
  background-size: 400%;
  transition: background 300ms ease-in-out;
}
.fourth:hover {
  background-position: 0;
}

.fifth {
  border-color: #8e44ad;
  border-radius: 0;
  color: #8e44ad;
  position: relative;
  overflow: hidden;
  z-index: 1;
  transition: color 150ms ease-in-out;
}
.fifth:after {
  content: '';
  position: absolute;
  display: block;
  top: 0;
  left: 50%;
  -webkit-transform: translateX(-50%);
          transform: translateX(-50%);
  width: 0;
  height: 100%;
  background: #8e44ad;
  z-index: -1;
  transition: width 150ms ease-in-out;
}
.fifth:hover {
  color: #fff;
}
.fifth:hover:after {
  width: 110%;
}

.sixth {
  border-radius: 3em;
  border-color: #2ecc71;
  color: #2ecc71;
  background-image: linear-gradient(to bottom, transparent 50%, #2ecc71 50%);
  background-position: 0% 0%;
  background-size: 210%;
  transition: background 150ms ease-in-out, color 150ms ease-in-out;
}
.sixth:hover {
  color: #fff;
  background-position: 0 100%;
}