CSS Tutorial – CSS Only Border Animation

Rengga Dev – CSS-only border animation on hover. It needs a solid background in order to work.

.container
  a.border-animation(href="#")
    .border-animation__inner Border animation

@import url(https://fonts.googleapis.com/css?family=Six+Caps);

html * {
  box-sizing: border-box;
}

body {
  font-size: 16px;
  padding: 10px;
  background: #333333;
  color: #ffffff;
  text-align: center;
  height: 100vh;
  margin: 0;
  display: flex;
  align-items: center;
  height: 100vh;
}

.container {
  width: 100%;
}

.border-animation {
  --border-width: 0.1em;
  --animation-speed: 0.5s;
  --color: #ffffff;
  color: var(--color);
  position: relative;
  display: inline-block;
  font-size: 4em;
  line-height: 1em;
  transform: scale(1, 0.8);
  border: var(--border-width) solid transparent;
  
  .border-animation__inner {
    position: relative;
    display: inline-block;
    width: 100%;
    font-family: 'Six Caps', sans-serif;
    font-weight: 300;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    cursor: pointer;
    padding: 0.2em;
    // background: rgba(50, 50, 50, 0.5);
    background: #333;
    z-index: 1;
    border: solid var(--border-width) transparent;
  }
  
  &:before,
  &:after {
    content: '';
    position: absolute;
    background: var(--color);
  }
  
  &:focus:before,
  &:hover:before {
    animation: beforeBorders var(--animation-speed) forwards ease-in-out;
  }

  &:focus:after,
  &:hover:after {
    animation: afterBorders var(--animation-speed) forwards ease-in-out;
  }
  
  &:focus,
  &:hover {
    animation: borderColors var(--animation-speed) steps(1) forwards;
    outline: none;

    .border-animation__inner {
      animation: background calc(var(--animation-speed) / 5 * 3) forwards ease-in-out;
      animation-delay: calc(var(--animation-speed) / 5 * 2);
    }
  }
}

@keyframes beforeBorders {
  0% {
    top: calc(var(--border-width) * -1);
    left: 50%;
    bottom: auto;
    right: auto;
    width: 0;
    height: var(--border-width);
  }
  33% {    
    top: calc(var(--border-width) * -1);
    left: calc(var(--border-width) * -1);
    bottom: auto;
    right: auto;
    width: calc(var(--border-width) + 50%);
    height: var(--border-width);
  }
  66% {
    top: calc(var(--border-width) * -1);
    left: calc(var(--border-width) * -1);
    bottom: auto;
    right: auto;
    width: var(--border-width);
    height: calc((var(--border-width) * 2) + 100%);
  }
  100% {
    top: auto;
    left: calc(var(--border-width) * -1);
    bottom: calc(var(--border-width) * -1);
    right: auto;
    width: calc(var(--border-width) + 50%);
    height: calc((var(--border-width) * 2) + 100%);
  }
}

@keyframes afterBorders {
  0% {
    top: calc(var(--border-width) * -1);
    left: auto;
    bottom: auto;
    right: 50%;
    width: 0;
    height: var(--border-width);
  }
  33% {    
    top: calc(var(--border-width) * -1);
    left: auto;
    bottom: auto;
    right: calc(var(--border-width) * -1);
    width: calc(var(--border-width) + 50%);
    height: var(--border-width);
  }
  66% {
    top: calc(var(--border-width) * -1);
    left: auto;
    bottom: auto;
    right: calc(var(--border-width) * -1);
    width: var(--border-width);
    height: calc((var(--border-width) * 2) + 100%);
  }
  100% {
    top: auto;
    left: auto;
    bottom: calc(var(--border-width) * -1);
    right: calc(var(--border-width) * -1);
    width: calc(var(--border-width) + 50%);
    height: calc((var(--border-width) * 2) + 100%);
  }
}

@keyframes borderColors {
  0% {
    border-top-color: transparent;
    border-right-color: transparent;
    border-bottom-color: transparent;
    border-left-color: transparent;
  }
  33% {
    border-top-color: var(--color);
    border-right-color: transparent;
    border-bottom-color: transparent;
    border-left-color: transparent;

  }
  66% {
    border-top-color: var(--color);
    border-right-color: var(--color);
    border-bottom-color: transparent;
    border-left-color: var(--color);
  }
  100% {
    border-top-color: var(--color);
    border-right-color: var(--color);
    border-bottom-color: var(--color);
    border-left-color: var(--color);
  }
}

@keyframes background {
  to {
    background: #555;
    text-shadow: 0 0.1em 0.1em #111;
  }
}

@media (min-width: 850px) {
  body {
    justify-content: center;
  }
}

@media (min-width: 1200px) {
  .border-animation {
    font-size: 6em;
    line-height: 1em;    
  }
}