CSS: repeated animated background - css

Question

I'm trying to create a repeated background existing out of two parts. Each part is a gradient and while the one moves up, the other moves down.
The best I got is this:
html {
background: black;
color: #4c4c4c;
}
body {
margin: 30vh auto;
max-width: 80vw;
}
.wave {
background: none;
height: 1rem;
width: 50%;
position: absolute;
z-index: 2;
animation: move 700ms 0ms steps(2) infinite both;
}
.color::after,
.color::before {
content: "";
position: absolute;
left: 0;
right: 0;
height: 100%;
top: 0;
}
.color {
background-image: linear-gradient(#fe0000 50%, #6531ff 0 100%);
}
.color::after {
background: linear-gradient(to bottom, #f4e04d, #3bceac 20%, rgba(22, 22, 22, 0) 100%), linear-gradient(to right, #042a2b 3rem, transparent 3rem, transparent 6rem);
}
.wave,
.color::after,
.color::before {
background-size: 5rem 1rem;
background-repeat: repeat-x;
}
#keyframes move {
0% {
margin-top: -3rem;
}
100% {
margin-top: -3.25rem;
}
}
<div class="color wave"></div>
I get why this doesn't work, but not sure how to proceed.
Since it is difficult to describe, here is an image of what I'm looking for:
At first (position 1), all odd blocks are higher than the even blocks. After the first animation, it's the other way around (position 2) and so on.

Answer 1

Maybe like below:
.box {
height:100px;
background:linear-gradient(red,blue,yellow,red) 0 0/100% 200%;
animation:y 2s linear infinite;
}
.box::after {
content:"";
display:block;
height:100%;
background:linear-gradient(green,lightblue,pink,green) 0 0/100% 200%;
animation:inherit;
animation-direction: reverse;
-webkit-mask:linear-gradient(90deg,#fff 50%,transparent 0) 0 0/20% 100%;
}
#keyframes y {
to {
background-position:0 -200%;
}
}
<div class="box"></div>

Answer 2

UPDATE: This is an interesting problem. I'm surprised to find that I don't have an obvious or particularly elegant solution to having a gradient running vertically while repeating with horizontal gaps.
Far more elusive than I initially expected.
Best I could come up with is to put one of the gradients in a pseudo element and apply a mask-image. This won't work in IE, but it appears to be supported everywhere else.
See updated demo below.
If I understand what you're trying to do, I think you could accomplish it by animating the background positions:
.demo {
height: 200px;
background-image:
linear-gradient(#f4e04d, #3bceac 20%, rgba(22, 22, 22, 0) 100%);
animation: move 0.7s infinite alternate;
background-size: 3rem;
position: relative;
}
.demo::before {
content: '';
position: absolute;
top: 0;
left: 0;
bottom: 0;
right: 0;
background: linear-gradient(#042a2b, transparent);
/* This is the magic part: using a horizontal repeating-linear-gradient
to mask out "columns", allowing the container's background gradient to
show through */
-webkit-mask-image: repeating-linear-gradient(to right, black 0 3rem, transparent 3rem 6rem);
background-size: 3rem;
/* run the same animation in reverse to animate up instead of down */
animation: move 0.7s infinite alternate-reverse;
}
#keyframes move {
from {
background-position: 0 0;
}
to {
background-position:
0 200px;
}
}
<div class="demo"></div>

Answer 3

It's difficult to infer exactly what you're trying to do, but here's another sample (very similar to #ray hatfield's answer) that will move the first background down while the second background moves up:
.sample {
width: 250px;
height: 50px;
position: relative;
background-image: linear-gradient(to bottom, #f4e04d, #3bceac 20%, rgba(22, 22, 22, 0) 100%), linear-gradient(to right, #042a2b 3rem, transparent 3rem, transparent 6rem);
animation: move 1s infinite linear;
}
#keyframes move {
0%, 100% {
background-position: 0 -75px, 0 0;
}
50% {
background-position: 0 0, 0 -75px;
}
}
<div class="sample"></div>