Neon Buttons/neon_button.css
body {
  background: black;
}
.first {
  background-color: #031321;
}
.first a {
  display: inline-block;
  position: relative;
  font-size: 24px;
  padding: 15px 30px;
  color: #2196f3;
  text-decoration: none;
  text-transform: uppercase;
  overflow: hidden;
  letter-spacing: 4px;
  transition: 0.2s;
}

.third {
  background: #050801;
  padding: 20px;
  margin: 20px;
  display: flex;
  flex-direction: column;
}

.third a {
  display: inline-block;
  position: relative;
  font-size: 24px;
  padding: 15px 30px;
  color: #03e9f4;
  text-decoration: none;
  text-transform: uppercase;
  overflow: hidden;
  letter-spacing: 4px;
  transition: 0.2s;
}

.first a:hover {
  color: #255784;
  background: #2196f3;
  box-shadow: 0 0 10px #2196f3, 0 0 40px #2196f3, 0 0 80px #2196f3;
  transition-delay: 1s;
}

.third a:hover {
  color: #050801;
  background: #03e9f4;
  box-shadow: 0 0 10px #2196f3, 0 0 40px #2196f3, 0 0 80px #2196f3;
  transition-delay: 0.5s;
}

a span {
  position: absolute;
  display: block;
}

a span:nth-child(1) {
  top: 0;
  left: -100%;
  width: 100%;
  height: 2px;
  background: linear-gradient(90deg, transparent, #2196f3);
}
a:hover span:nth-child(1) {
  left: 100%;
  transition: 1s;
}

a span:nth-child(3) {
  bottom: 0;
  right: -100%;
  width: 100%;
  height: 2px;
  background: linear-gradient(270deg, transparent, #2196f3);
}
a:hover span:nth-child(3) {
  right: 100%;
  transition: 1s;
  transition-delay: 0.5s;
}

a span:nth-child(2) {
  top: -100%;
  right: 0;
  width: 2px;
  height: 100%;
  background: linear-gradient(180deg, transparent, #2196f3);
}
a:hover span:nth-child(2) {
  top: 100%;
  transition: 1s;
  transition-delay: 0.25s;
}

a span:nth-child(4) {
  bottom: -100%;
  left: 0;
  width: 2px;
  height: 100%;
  background: linear-gradient(180deg, transparent, #2196f3);
}
a:hover span:nth-child(4) {
  bottom: 100%;
  transition: 1s;
  transition-delay: 0.75s;
}

.third a:nth-child(1) {
  filter: hue-rotate(290deg);
}
.third a:nth-child(2) {
  filter: hue-rotate(230deg);
}
.third a:nth-child(3) {
  filter: hue-rotate(110deg);
}
.third a:nth-child(4) {
  filter: hue-rotate(0deg);
}
.third a:nth-child(5) {
  filter: hue-rotate(45deg);
}
.third a:nth-child(6) {
  filter: hue-rotate(90deg);
}
