JSFiddle - React, Tailwind, and code Playground

by Morgan Gilroy

HTML

<h1>CSS Border Animation</h1>
<div id="testBox" class="testBox borderTransition">
  Lorem ipsum dolor sit amet, consectetur adipiscing elit. Integer lacus purus, interdum in sem sed, dapibus lobortis erat.
</div>
<BR />
<div id="testBox2" class="testBox borderAnimation">
  Lorem ipsum dolor sit amet, consectetur adipiscing elit. Integer lacus purus, interdum in sem sed, dapibus lobortis erat.
</div>
<BR />
<div id="testBox3" class="testBox borderAnimation2">
  Lorem ipsum dolor sit amet, consectetur adipiscing elit. Integer lacus purus, interdum in sem sed, dapibus lobortis erat.
</div>

CSS

html {
  background: #fafafa;
}

body {
  color: #4b507a;
  font: 300 24px/1.5 Lato, sans-serif;
  margin: 1em auto;
  max-width: 36em;
  padding: 1em 1em 2em;
  text-align: center;
}

h1 {
  font-weight: 300;
  font-size: 2.5em;
}

.testBox {
  border-radius: 3px;
  background-color: #EaEaEa;
  box-shadow: inset 0 0 0 2px #4286f4;
  min-height: 100px;
  transition: 0.25s;
  padding: 10px;
}

.testBox:hover {
  background-color: #dadada
}

.borderTransition {
  border: 0;
  box-sizing: border-box;
  position: relative;
}

.borderTransition::before,
.borderTransition::after {
  box-sizing: inherit;
  content: '';
  position: absolute;
  border: 2px solid transparent;
  width: 0px;
  height: 0px;
}

.borderTransition::before {
  top: 0;
  left: 0;
}

.borderTransition::after {
  bottom: 0;
  right: 0;
}

.borderTransition:hover::before,
.borderTransition:hover::after {
  width: 100%;
  height: 100%;
}

.borderTransition:hover::before {
  border-top-color: #42cbf4;
  border-right-color: #42cbf4;
  /*transition: width 0.25s ease-out, height 0.25s ease-out 0.25s;*/
  transition: width 0.5s ease-out, height 0.5s ease-out 0.5s;
}

.borderTransition:hover::after {
  border-bottom-color: #42cbf4;
  border-left-color: #42cbf4;
  transition: border-color 0s ease-out 1s, width 0.5s ease-out 1s, height 0.5s ease-out 1.5s;
}

@keyframes topRight {
  0% {
    left: 0%;
    top: 0%;
    width: 0%;
    height: 0%;
  }
  25% {
    left: 0%;
    top: 0%;
    width: 100%;
    height: 0%;
  }
  50% {
    right: 0%;
    top: 0%;
    width: 100%;
    height: 100%;
  }
  75% {
    right: 0%;
    bottom: 0%;
    width: 0%;
    height: 100%;
  }
  100% {
    right: 0%;
    bottom: 0%;
    width: 0%;
    height: 0%;
  }
}

@keyframes bottomLeft {
  0% {
    right: 0%;
    bottom: 0%;
    width: 0%;
    height: 0%;
  }
  25% {
    right: 0%;
    bottom: 0%;
    width: 100%;
    height: 0%;
  }
  50% {
    right: 0%;
    bottom: 0%;
    width: 100%;
    height: 100%;
  }
  75% {
    right:...