How to create running text (marquee) using CSS

Question

I face quite big stuck while studying CSS animation.

I'm going to make a "transform: translate" animation which shows text that overflow content width like below situation.
How it works?: (Youtube video link)

var div1 = document.getElementById("div1");
var cont = document.getElementById("content");
var inf = document.getElementById("inf");

inf.innerHTML = "<p> Does the text inside h1 cut off? : " + (cont.offsetWidth < cont.scrollWidth) +
  "<br><b>Length of text overflow</b>: " + (cont.offsetWidth - cont.scrollWidth) +
  "<br> h1 width: " + (cont.offsetWidth) + ", h1's text length: " + (cont.scrollWidth) + "</p>";


div1.style.backgroundColor = "#A13DAF";
cont.style.webkitAnimationName = "moving";
cont.style.animationName = "moving";

cont.style.animationDuration = "3s";
cont.style.webkitAnimationDuration = "3s";

cont.style.animationTimingFunction = "linear";
cont.style.webkitAnimationTimingFunction = "linear";

#div1 {
  margin: 10px;
  width: 300px;
  background: rgb(40, 40, 40);
  white-space: nowrap;
  overflow: hidden;
}

#content {
  color: white;
  width: 100%;
  /* animation-name: moving;
    animation-duration: 3s;
    animation-timing-function: linear;
    -webkit-animation-name: moving;
    -webkit-animation-duration: 3s;
    -webkit-animation-timing-function: linear; */
}

@keyframes moving {
  0% {
    transform: none;
    -webkit-transform: none;
  }
  65% {
    /*below code is pseudo code, It doesn't work,
          It is an explanation of the direction I want but.. I can't find way to ...ㅠㅠ*/
    transform: translate( calc(#content.scrollWidth - #content.offsetWidth), 0);
    -webkit-transform: translate( calc(#content.scrollWidth - #content.offsetWidth), 0);
    /*below value is caculated value of fixed text length and content width,
          but if either of these changes, this code will not be available for my purpose.
          Is there any way to specific values of CSS elements?*/
    transform: translate( -668px, 0);
    -webkit-transform: translate( -668px, 0);
  }
  100% {
    transform: translate( -668px, 0);
    -webkit-transform: translate( -668px, 0);
  }
}

<div id="div1">
  <h1 id="content">
    The only thing that matters now is everything You think of me
  </h1>
</div>
<div id="inf"></div>

Like Above code,
I want to make the text to move left in the content (h1), as much as the amount of the cut off cause of its overflow.
But, I can't find a way to refer values of content in CSS.

Is there any way to modify a CSS value by referring to a specific value of another element in the CSS without JavaScript?

I try to avoid the method of changing the keyframe using Javascript as much as possible, though it can be quite heavy.

Thank you very much.

Answer 1

You could animate both transform and simultaneously the margin-left so that the animation will end exactly at the text-end:

.marquee {
  position: relative;
  overflow: hidden;
  background: rgb(161, 61, 175);
  color: #fff;
}

.marquee span {
  display: inline-block;
  min-width: 100%; /* this is to prevent shorter text animate to right */
  white-space: nowrap;
  font-size: 2.5em;
  animation: marquee 4s ease-in-out forwards;
}

@keyframes marquee {
  from {transform: translateX(0);     margin-left: 0;}
  to   {transform: translateX(-100%); margin-left: 100%; }
}

<h1 class="marquee">
  <span>The only thing that matters now is everything You think of me</span>
</h1>

<p class="marquee">
  <span>Beware of short texts!</span>
</p>

Answer 2

Here is another idea with only transform used as animation:

.marquee {
  overflow: hidden;
  background: rgb(161, 61, 175);
  color: #fff;
}

.marquee > span {
  display:block;
  animation: marquee 4s ease-in-out;
  transform: translateX(100%);
}
.marquee > * > span {
  display: inline-block;
  min-width: 100%;
  white-space: nowrap;
  font-size: 2.5em;
  animation:inherit;
  transform: translateX(-100%);
}

@keyframes marquee {
  from {
    transform: translateX(0);
  }
}

<h1 class="marquee">
  <span>
    <span>The only thing that matters now is everything You think of me</span>
  </span>
</h1>

<h1 class="marquee">
  <span>
    <span>The only thing that matters now is everything</span>
  </span>
</h1>

<p class="marquee">
  <span>
    <span>Beware of short texts!</span>
  </span>
</p>