Animated diagonal border effect

Animated diagonal border effect

by Csaba Hellinger

HTML

<div class="outer">
<div class="inner">
  <h1>Hello</h1>
  <p>Check out this sick ass border effect around this box.</p>
</div>
</div>

CSS

body {
  background: #AAA;
  padding: 5rem;
  font-family: sans-serif;
  --border: #B00;
  --bg: white;
  --size: 2rem;
}

.outer {
  padding: 0.5rem;
  width: 17rem;
  text-align: center;
  background: linear-gradient(-45deg, 
    var(--bg) 0%,
    var(--bg) 25%,
    var(--border) 25%,
    var(--border) 50%,
    var(--bg) 50%,
    var(--bg) 75%,
    var(--border) 75%,
    var(--border) 100%    
  );
  color: var(--border);
  background-size: var(--size) var(--size);
  border: 0.1rem solid var(--border);
  box-shadow: 0.3rem 0.3rem 0.5rem 0.1rem #0004;
  animation: slide 1s linear infinite;
}

.inner {
  background: white;
  padding: 1rem;
  border: 0.1rem solid var(--border);
  box-sizing: border-box;
}

@keyframes slide {
  0% { background-position: 0; }
  100% { background-position: var(--size); }  
}