Rainbow text animation using only CSS - html

Question

I got inspired by this Rainbow Text Animation rainbow-text-animation, and I would like to use only CSS to make this happen instead of all that complicated SCSS coding.
I got what I like so far and now I just want to make it go from left to right AND having multiple colors in one entire line instead of one color at a time.
Run the code snippet to see what I'm talking about.
So as you can see, I want as many colors I want in one line and not one color in the entire line (one at a time).
#shadowBox {
background-color: rgb(0, 0, 0);
/* Fallback color */
background-color: rgba(0, 0, 0, 0.2);
/* Black w/opacity/see-through */
border: 3px solid;
}
.rainbow {
text-align: center;
text-decoration: underline;
font-size: 32px;
font-family: monospace;
letter-spacing: 5px;
animation: colorRotate 6s linear 0s infinite;
}
#keyframes colorRotate {
from {
color: #6666ff;
}
10% {
color: #0099ff;
}
50% {
color: #00ff00;
}
75% {
color: #ff3399;
}
100% {
color: #6666ff;
}
}
<div id="shadowBox">
<h3 class="rainbow">COMING SOON</h3>
</div>

Answer 1

You can achieve this effect by using a moving gradient background, color to transparent, and background clip to text.
#shadowBox {
background-color: rgb(0, 0, 0);
/* Fallback color */
background-color: rgba(0, 0, 0, 0.2);
/* Black w/opacity/see-through */
border: 3px solid;
}
.rainbow {
text-align: center;
text-decoration: underline;
font-size: 32px;
font-family: monospace;
letter-spacing: 5px;
}
.rainbow_text_animated {
background: linear-gradient(to right, #6666ff, #0099ff , #00ff00, #ff3399, #6666ff);
-webkit-background-clip: text;
background-clip: text;
color: transparent;
animation: rainbow_animation 6s ease-in-out infinite;
background-size: 400% 100%;
}
#keyframes rainbow_animation {
0%,100% {
background-position: 0 0;
}
50% {
background-position: 100% 0;
}
}
<div id="shadowBox">
<h3 class="rainbow rainbow_text_animated">COMING SOON</h3>
</div>

Answer 2

#shadowBox {
background-color: rgb(0, 0, 0);
/* Fallback color */
background-color: rgba(0, 0, 0, 0.2);
/* Black w/opacity/see-through */
border: 3px solid;
}
.rainbow {
text-align: center;
text-decoration: underline;
font-size: 32px;
font-family: monospace;
letter-spacing: 5px;
animation: colorRotate .5s linear 0s infinite;
}
#keyframes colorRotate {
from {
color: #6666ff;
}
10% {
color: #0099ff;
}
50% {
color: #00ff00;
}
75% {
color: #ff3399;
}
100% {
color: #6666ff;
}
}
<div id="shadowBox">
<h3 class="rainbow">VERB</h3>
</div>