CSS horizontal line animation (gradient colors)

Question

I have colored, animated, vertical line like this one:

@keyframes colored {
  0% {
    background-image: -webkit-linear-gradient(left, #c4e17f, #c4e17f 12.5%, #f7fdca 12.5%, #f7fdca 25%, #fecf71 25%, #fecf71 37.5%, #f0776c 37.5%, #f0776c 50%, #db9dbe 50%, #db9dbe 62.5%, #c49cde 62.5%, #c49cde 75%, #669ae1 75%, #669ae1 87.5%, #62c2e4 87.5%, #62c2e4);
    background-image: -moz-linear-gradient(left, #c4e17f, #c4e17f 12.5%, #f7fdca 12.5%, #f7fdca 25%, #fecf71 25%, #fecf71 37.5%, #f0776c 37.5%, #f0776c 50%, #db9dbe 50%, #db9dbe 62.5%, #c49cde 62.5%, #c49cde 75%, #669ae1 75%, #669ae1 87.5%, #62c2e4 87.5%, #62c2e4);
    background-image: -o-linear-gradient(left, #c4e17f, #c4e17f 12.5%, #f7fdca 12.5%, #f7fdca 25%, #fecf71 25%, #fecf71 37.5%, #f0776c 37.5%, #f0776c 50%, #db9dbe 50%, #db9dbe 62.5%, #c49cde 62.5%, #c49cde 75%, #669ae1 75%, #669ae1 87.5%, #62c2e4 87.5%, #62c2e4);
    background-image: linear-gradient(to right, #c4e17f, #c4e17f 12.5%, #f7fdca 12.5%, #f7fdca 25%, #fecf71 25%, #fecf71 37.5%, #f0776c 37.5%, #f0776c 50%, #db9dbe 50%, #db9dbe 62.5%, #c49cde 62.5%, #c49cde 75%, #669ae1 75%, #669ae1 87.5%, #62c2e4 87.5%, #62c2e4);
  }
  12.5% {
    background-image: -webkit-linear-gradient(left, #62c2e4, #62c2e4 12.5%, #c4e17f 12.5%, #c4e17f 25%, #f7fdca 25%, #f7fdca 37.5%, #fecf71 37.5%, #fecf71 50%, #f0776c 50%, #f0776c 62.5%, #db9dbe 62.5%, #db9dbe 75%, #c49cde 75%, #c49cde 87.5%, #669ae1 87.5%, #669ae1);
    background-image: -moz-linear-gradient(left, #62c2e4, #62c2e4 12.5%, #c4e17f 12.5%, #c4e17f 25%, #f7fdca 25%, #f7fdca 37.5%, #fecf71 37.5%, #fecf71 50%, #f0776c 50%, #f0776c 62.5%, #db9dbe 62.5%, #db9dbe 75%, #c49cde 75%, #c49cde 87.5%, #669ae1 87.5%, #669ae1);
    background-image: -o-linear-gradient(left, #62c2e4, #62c2e4 12.5%, #c4e17f 12.5%, #c4e17f 25%, #f7fdca 25%, #f7fdca 37.5%, #fecf71 37.5%, #fecf71 50%, #f0776c 50%, #f0776c 62.5%, #db9dbe 62.5%, #db9dbe 75%, #c49cde 75%, #c49cde 87.5%, #669ae1 87.5%, #669ae1);
    background-image: linear-gradient(to right, #62c2e4, #62c2e4 12.5%, #c4e17f 12.5%, #c4e17f 25%, #f7fdca 25%, #f7fdca 37.5%, #fecf71 37.5%, #fecf71 50%, #f0776c 50%, #f0776c 62.5%, #db9dbe 62.5%, #db9dbe 75%, #c49cde 75%, #c49cde 87.5%, #669ae1 87.5%, #669ae1);
  }
  25% {
    background-image: -webkit-linear-gradient(left, #669ae1, #669ae1 12.5%, #62c2e4 12.5%, #62c2e4 25%, #c4e17f 25%, #c4e17f 37.5%, #f7fdca 37.5%, #f7fdca 50%, #fecf71 50%, #fecf71 62.5%, #f0776c 62.5%, #f0776c 75%, #db9dbe 75%, #db9dbe 87.5%, #c49cde 87.5%, #c49cde);
    background-image: -moz-linear-gradient(left, #669ae1, #669ae1 12.5%, #62c2e4 12.5%, #62c2e4 25%, #c4e17f 25%, #c4e17f 37.5%, #f7fdca 37.5%, #f7fdca 50%, #fecf71 50%, #fecf71 62.5%, #f0776c 62.5%, #f0776c 75%, #db9dbe 75%, #db9dbe 87.5%, #c49cde 87.5%, #c49cde);
    background-image: -o-linear-gradient(left, #669ae1, #669ae1 12.5%, #62c2e4 12.5%, #62c2e4 25%, #c4e17f 25%, #c4e17f 37.5%, #f7fdca 37.5%, #f7fdca 50%, #fecf71 50%, #fecf71 62.5%, #f0776c 62.5%, #f0776c 75%, #db9dbe 75%, #db9dbe 87.5%, #c49cde 87.5%, #c49cde);
    background-image: linear-gradient(to right, #669ae1, #669ae1 12.5%, #62c2e4 12.5%, #62c2e4 25%, #c4e17f 25%, #c4e17f 37.5%, #f7fdca 37.5%, #f7fdca 50%, #fecf71 50%, #fecf71 62.5%, #f0776c 62.5%, #f0776c 75%, #db9dbe 75%, #db9dbe 87.5%, #c49cde 87.5%, #c49cde);
  }
  37.5% {
    background-image: -webkit-linear-gradient(left, #c49cde, #c49cde 12.5%, #669ae1 12.5%, #669ae1 25%, #62c2e4 25%, #62c2e4 37.5%, #c4e17f 37.5%, #c4e17f 50%, #f7fdca 50%, #f7fdca 62.5%, #fecf71 62.5%, #fecf71 75%, #f0776c 75%, #f0776c 87.5%, #db9dbe 87.5%, #db9dbe);
    background-image: -moz-linear-gradient(left, #c49cde, #c49cde 12.5%, #669ae1 12.5%, #669ae1 25%, #62c2e4 25%, #62c2e4 37.5%, #c4e17f 37.5%, #c4e17f 50%, #f7fdca 50%, #f7fdca 62.5%, #fecf71 62.5%, #fecf71 75%, #f0776c 75%, #f0776c 87.5%, #db9dbe 87.5%, #db9dbe);
    background-image: -o-linear-gradient(left, #c49cde, #c49cde 12.5%, #669ae1 12.5%, #669ae1 25%, #62c2e4 25%, #62c2e4 37.5%, #c4e17f 37.5%, #c4e17f 50%, #f7fdca 50%, #f7fdca 62.5%, #fecf71 62.5%, #fecf71 75%, #f0776c 75%, #f0776c 87.5%, #db9dbe 87.5%, #db9dbe);
    background-image: linear-gradient(to right, #c49cde, #c49cde 12.5%, #669ae1 12.5%, #669ae1 25%, #62c2e4 25%, #62c2e4 37.5%, #c4e17f 37.5%, #c4e17f 50%, #f7fdca 50%, #f7fdca 62.5%, #fecf71 62.5%, #fecf71 75%, #f0776c 75%, #f0776c 87.5%, #db9dbe 87.5%, #db9dbe);
  }
  50% {
    background-image: -webkit-linear-gradient(left, #db9dbe, #db9dbe 12.5%, #c49cde 12.5%, #c49cde 25%, #669ae1 25%, #669ae1 37.5%, #62c2e4 37.5%, #62c2e4 50%, #c4e17f 50%, #c4e17f 62.5%, #f7fdca 62.5%, #f7fdca 75%, #fecf71 75%, #fecf71 87.5%, #f0776c 87.5%, #f0776c);
    background-image: -moz-linear-gradient(left, #db9dbe, #db9dbe 12.5%, #c49cde 12.5%, #c49cde 25%, #669ae1 25%, #669ae1 37.5%, #62c2e4 37.5%, #62c2e4 50%, #c4e17f 50%, #c4e17f 62.5%, #f7fdca 62.5%, #f7fdca 75%, #fecf71 75%, #fecf71 87.5%, #f0776c 87.5%, #f0776c);
    background-image: -o-linear-gradient(left, #db9dbe, #db9dbe 12.5%, #c49cde 12.5%, #c49cde 25%, #669ae1 25%, #669ae1 37.5%, #62c2e4 37.5%, #62c2e4 50%, #c4e17f 50%, #c4e17f 62.5%, #f7fdca 62.5%, #f7fdca 75%, #fecf71 75%, #fecf71 87.5%, #f0776c 87.5%, #f0776c);
    background-image: linear-gradient(to right, #db9dbe, #db9dbe 12.5%, #c49cde 12.5%, #c49cde 25%, #669ae1 25%, #669ae1 37.5%, #62c2e4 37.5%, #62c2e4 50%, #c4e17f 50%, #c4e17f 62.5%, #f7fdca 62.5%, #f7fdca 75%, #fecf71 75%, #fecf71 87.5%, #f0776c 87.5%, #f0776c);
  }
  62.5% {
    background-image: -webkit-linear-gradient(left, #f0776c, #f0776c 12.5%, #db9dbe 12.5%, #db9dbe 25%, #c49cde 25%, #c49cde 37.5%, #669ae1 37.5%, #669ae1 50%, #62c2e4 50%, #62c2e4 62.5%, #c4e17f 62.5%, #c4e17f 75%, #f7fdca 75%, #f7fdca 87.5%, #fecf71 87.5%, #fecf71);
    background-image: -moz-linear-gradient(left, #f0776c, #f0776c 12.5%, #db9dbe 12.5%, #db9dbe 25%, #c49cde 25%, #c49cde 37.5%, #669ae1 37.5%, #669ae1 50%, #62c2e4 50%, #62c2e4 62.5%, #c4e17f 62.5%, #c4e17f 75%, #f7fdca 75%, #f7fdca 87.5%, #fecf71 87.5%, #fecf71);
    background-image: -o-linear-gradient(left, #f0776c, #f0776c 12.5%, #db9dbe 12.5%, #db9dbe 25%, #c49cde 25%, #c49cde 37.5%, #669ae1 37.5%, #669ae1 50%, #62c2e4 50%, #62c2e4 62.5%, #c4e17f 62.5%, #c4e17f 75%, #f7fdca 75%, #f7fdca 87.5%, #fecf71 87.5%, #fecf71);
    background-image: linear-gradient(to right, #f0776c, #f0776c 12.5%, #db9dbe 12.5%, #db9dbe 25%, #c49cde 25%, #c49cde 37.5%, #669ae1 37.5%, #669ae1 50%, #62c2e4 50%, #62c2e4 62.5%, #c4e17f 62.5%, #c4e17f 75%, #f7fdca 75%, #f7fdca 87.5%, #fecf71 87.5%, #fecf71);
  }
  75% {
    background-image: -webkit-linear-gradient(left, #fecf71, #fecf71 12.5%, #f0776c 12.5%, #f0776c 25%, #db9dbe 25%, #db9dbe 37.5%, #c49cde 37.5%, #c49cde 50%, #669ae1 50%, #669ae1 62.5%, #62c2e4 62.5%, #62c2e4 75%, #c4e17f 75%, #c4e17f 87.5%, #f7fdca 87.5%, #f7fdca);
    background-image: -moz-linear-gradient(left, #fecf71, #fecf71 12.5%, #f0776c 12.5%, #f0776c 25%, #db9dbe 25%, #db9dbe 37.5%, #c49cde 37.5%, #c49cde 50%, #669ae1 50%, #669ae1 62.5%, #62c2e4 62.5%, #62c2e4 75%, #c4e17f 75%, #c4e17f 87.5%, #f7fdca 87.5%, #f7fdca);
    background-image: -o-linear-gradient(left, #fecf71, #fecf71 12.5%, #f0776c 12.5%, #f0776c 25%, #db9dbe 25%, #db9dbe 37.5%, #c49cde 37.5%, #c49cde 50%, #669ae1 50%, #669ae1 62.5%, #62c2e4 62.5%, #62c2e4 75%, #c4e17f 75%, #c4e17f 87.5%, #f7fdca 87.5%, #f7fdca);
    background-image: linear-gradient(to right, #fecf71, #fecf71 12.5%, #f0776c 12.5%, #f0776c 25%, #db9dbe 25%, #db9dbe 37.5%, #c49cde 37.5%, #c49cde 50%, #669ae1 50%, #669ae1 62.5%, #62c2e4 62.5%, #62c2e4 75%, #c4e17f 75%, #c4e17f 87.5%, #f7fdca 87.5%, #f7fdca);
  }
  87.5% {
    background-image: -webkit-linear-gradient(left, #f7fdca, #f7fdca 12.5%, #fecf71 12.5%, #fecf71 25%, #f0776c 25%, #f0776c 37.5%, #db9dbe 37.5%, #db9dbe 50%, #c49cde 50%, #c49cde 62.5%, #669ae1 62.5%, #669ae1 75%, #62c2e4 75%, #62c2e4 87.5%, #c4e17f 87.5%, #c4e17f);
    background-image: -moz-linear-gradient(left, #f7fdca, #f7fdca 12.5%, #fecf71 12.5%, #fecf71 25%, #f0776c 25%, #f0776c 37.5%, #db9dbe 37.5%, #db9dbe 50%, #c49cde 50%, #c49cde 62.5%, #669ae1 62.5%, #669ae1 75%, #62c2e4 75%, #62c2e4 87.5%, #c4e17f 87.5%, #c4e17f);
    background-image: -o-linear-gradient(left, #f7fdca, #f7fdca 12.5%, #fecf71 12.5%, #fecf71 25%, #f0776c 25%, #f0776c 37.5%, #db9dbe 37.5%, #db9dbe 50%, #c49cde 50%, #c49cde 62.5%, #669ae1 62.5%, #669ae1 75%, #62c2e4 75%, #62c2e4 87.5%, #c4e17f 87.5%, #c4e17f);
    background-image: linear-gradient(to right, #f7fdca, #f7fdca 12.5%, #fecf71 12.5%, #fecf71 25%, #f0776c 25%, #f0776c 37.5%, #db9dbe 37.5%, #db9dbe 50%, #c49cde 50%, #c49cde 62.5%, #669ae1 62.5%, #669ae1 75%, #62c2e4 75%, #62c2e4 87.5%, #c4e17f 87.5%, #c4e17f);
  }
  100% {
    background-image: -webkit-linear-gradient(left, #c4e17f, #c4e17f 12.5%, #f7fdca 12.5%, #f7fdca 25%, #fecf71 25%, #fecf71 37.5%, #f0776c 37.5%, #f0776c 50%, #db9dbe 50%, #db9dbe 62.5%, #c49cde 62.5%, #c49cde 75%, #669ae1 75%, #669ae1 87.5%, #62c2e4 87.5%, #62c2e4);
    background-image: -moz-linear-gradient(left, #c4e17f, #c4e17f 12.5%, #f7fdca 12.5%, #f7fdca 25%, #fecf71 25%, #fecf71 37.5%, #f0776c 37.5%, #f0776c 50%, #db9dbe 50%, #db9dbe 62.5%, #c49cde 62.5%, #c49cde 75%, #669ae1 75%, #669ae1 87.5%, #62c2e4 87.5%, #62c2e4);
    background-image: -o-linear-gradient(left, #c4e17f, #c4e17f 12.5%, #f7fdca 12.5%, #f7fdca 25%, #fecf71 25%, #fecf71 37.5%, #f0776c 37.5%, #f0776c 50%, #db9dbe 50%, #db9dbe 62.5%, #c49cde 62.5%, #c49cde 75%, #669ae1 75%, #669ae1 87.5%, #62c2e4 87.5%, #62c2e4);
    background-image: linear-gradient(to right, #c4e17f, #c4e17f 12.5%, #f7fdca 12.5%, #f7fdca 25%, #fecf71 25%, #fecf71 37.5%, #f0776c 37.5%, #f0776c 50%, #db9dbe 50%, #db9dbe 62.5%, #c49cde 62.5%, #c49cde 75%, #669ae1 75%, #669ae1 87.5%, #62c2e4 87.5%, #62c2e4);
  }
}
.colored {
  margin-top: 5px;
  margin-bottom: 5px;
  height: 7px;
  border-top: 0;
  background: #c4e17f;
  border-radius: 5px;
  background-image: -webkit-linear-gradient(left, #c4e17f, #c4e17f 12.5%, #f7fdca 12.5%, #f7fdca 25%, #fecf71 25%, #fecf71 37.5%, #f0776c 37.5%, #f0776c 50%, #db9dbe 50%, #db9dbe 62.5%, #c49cde 62.5%, #c49cde 75%, #669ae1 75%, #669ae1 87.5%, #62c2e4 87.5%, #62c2e4);
  background-image: -moz-linear-gradient(left, #c4e17f, #c4e17f 12.5%, #f7fdca 12.5%, #f7fdca 25%, #fecf71 25%, #fecf71 37.5%, #f0776c 37.5%, #f0776c 50%, #db9dbe 50%, #db9dbe 62.5%, #c49cde 62.5%, #c49cde 75%, #669ae1 75%, #669ae1 87.5%, #62c2e4 87.5%, #62c2e4);
  background-image: -o-linear-gradient(left, #c4e17f, #c4e17f 12.5%, #f7fdca 12.5%, #f7fdca 25%, #fecf71 25%, #fecf71 37.5%, #f0776c 37.5%, #f0776c 50%, #db9dbe 50%, #db9dbe 62.5%, #c49cde 62.5%, #c49cde 75%, #669ae1 75%, #669ae1 87.5%, #62c2e4 87.5%, #62c2e4);
  background-image: linear-gradient(to right, #c4e17f, #c4e17f 12.5%, #f7fdca 12.5%, #f7fdca 25%, #fecf71 25%, #fecf71 37.5%, #f0776c 37.5%, #f0776c 50%, #db9dbe 50%, #db9dbe 62.5%, #c49cde 62.5%, #c49cde 75%, #669ae1 75%, #669ae1 87.5%, #62c2e4 87.5%, #62c2e4);
  animation-name: colored;
  animation-duration: 2s;
  animation-iteration-count: infinite;
}

<hr class="colored">

I'm wondering if it can be accomplished in some better (read: smarter way). It cost me some time to calculate and prepare all animation steps (was using excell) and I feel stupid.

Second question (based on one of the comments) is if this animation can be smoother? How to accomplish it?

Answer 1

Here is an example using the approach jcaron mentioned in his answer. You just use to copies of your horizontal line and place them next to each other, the last element before the first one. The parent element needs to be twice as wide as one of the hr elements. Then you can easily animate the parent element and don't have to redraw the linear-gradient within the animation.

@keyframes hr-animation {
  from{ transform: translate(0, 0); }
  to{ transform: translate(50%, 0); }
}
@-webkit-keyframes hr-animation {
  from{ -webkit-transform: translate(0, 0); }
  to{ -webkit-transform: translate(50%, 0); }
}
.hr-animation {
  -webkit-animation: hr-animation 5s linear infinite;
  animation: hr-animation 5s linear infinite;
}

body {
  margin: 10px 0 0 0;
  background: #555;
}

.colored {
  background-image: linear-gradient(left, #c4e17f, #c4e17f 12.5%, #f7fdca 12.5%, #f7fdca 25%, #fecf71 25%, #fecf71 37.5%, #f0776c 37.5%, #f0776c 50%, #db9dbe 50%, #db9dbe 62.5%, #c49cde 62.5%, #c49cde 75%, #669ae1 75%, #669ae1 87.5%, #62c2e4 87.5%, #62c2e4);
  background-image: -moz-linear-gradient(left, #c4e17f, #c4e17f 12.5%, #f7fdca 12.5%, #f7fdca 25%, #fecf71 25%, #fecf71 37.5%, #f0776c 37.5%, #f0776c 50%, #db9dbe 50%, #db9dbe 62.5%, #c49cde 62.5%, #c49cde 75%, #669ae1 75%, #669ae1 87.5%, #62c2e4 87.5%, #62c2e4);
  background-image: -o-linear-gradient(left, #c4e17f, #c4e17f 12.5%, #f7fdca 12.5%, #f7fdca 25%, #fecf71 25%, #fecf71 37.5%, #f0776c 37.5%, #f0776c 50%, #db9dbe 50%, #db9dbe 62.5%, #c49cde 62.5%, #c49cde 75%, #669ae1 75%, #669ae1 87.5%, #62c2e4 87.5%, #62c2e4);
  background-image: linear-gradient(to right, #c4e17f, #c4e17f 12.5%, #f7fdca 12.5%, #f7fdca 25%, #fecf71 25%, #fecf71 37.5%, #f0776c 37.5%, #f0776c 50%, #db9dbe 50%, #db9dbe 62.5%, #c49cde 62.5%, #c49cde 75%, #669ae1 75%, #669ae1 87.5%, #62c2e4 87.5%, #62c2e4);
}

.container {
  overflow: hidden;
  width: 100%;
}

.wrap {
  font-size: 0;
  height: 5px;
  width: 200%;
  position: relative;
}

.wrap hr {
  border: none;
  height: 5px;
  width: 50%;
  position: absolute;
}

.wrap hr:last-child {
  left: -50%;
}

<div class="container">
  <div class="wrap hr-animation">
    <hr class="colored ">
    <hr class="colored "> 
  </div>
</div>

Answer 2

Keeping your structure to the maximum, here is my solution

.colored {
  margin-top: 5px;
  margin-bottom: 5px;
  height: 7px;
  border-top: 0;
  background: #c4e17f;
  border-radius: 5px;
  background-image: linear-gradient(to right, #c4e17f, #c4e17f 12.5%, #f7fdca 12.5%, #f7fdca 25%, #fecf71 25%, #fecf71 37.5%, #f0776c 37.5%, #f0776c 50%, #db9dbe 50%, #db9dbe 62.5%, #c49cde 62.5%, #c49cde 75%, #669ae1 75%, #669ae1 87.5%, #62c2e4 87.5%, #62c2e4);
  padding-right: 50%;
  background-origin: content-box;
  background-size: 200%;
  animation-name: colored;
  animation-duration: 2s;
  animation-iteration-count: infinite;
  animation-timing-function: steps(8);
}

@keyframes colored {
  from {background-position: 0% 0%;}  
    to {background-position: 200% 0%;}
}

<hr class="colored">

I am animating the background position with a steps function, so the discrete change in colors is easily achieved.

A little bit trickier is the use of a single gradient, responsive, and animatable.

What would like as the easiest solution, stating that the background-size is 100%, is not affected by background-position changes in percentage.

The trick is to set the background on only half the element, (achieved with the padding trick) and then set the dimension to 200%