How can I achieve a CSS text loading animation over multiple lines?

Question

I am trying to implement a text loading animation with CSS. what I have is a text with black color, then when the page loads the text will fill start filling wi

Answer 1

An idea is to consider gradient coloration with an inline element. Simply pay attention to browser support of background-clip: text

body {
  background: #3498db;
  font-family: sans-serif;
}

h1 {
  font-size: 5em;
}

h1 span {
  background:
    linear-gradient(#fff,#fff) left no-repeat,
    rgba(0, 0, 0, .3);
  background-size:0% 100%;
  -webkit-background-clip: text;
  background-clip: text;
  -webkit-text-fill-color: transparent;
  color: transparent;
  animation:loading 5s forwards linear;
}

@keyframes loading {
  100% {
    background-size:100% 100%;
  }
}

<h1><span>Suspendisse mollis dolor vitae porta egestas. Nunc nec congue odio.</span></h1>

To better understand how it works, here is a basic example where you can see how inline element behave with background coloration and how its different from block level element:

.color {
  font-size: 1.5em;
  line-height: 1.5em;
  border: 2px solid;
  background: linear-gradient(red, red) left no-repeat;
  background-size: 0% 100%;
  animation: change 5s linear forwards;
}

@keyframes change {
  100% {
    background-size: 100% 100%
  }
}

<span class="color">
 lorem ipsume lorem ipsume lorem ipsume lorem ipsume lorem ipsume lorem ipsume lorem ipsume lorem ipsume lorem ipsume 
</span>
<div class="color">
  lorem ipsume lorem ipsume lorem ipsume lorem ipsume lorem ipsume lorem ipsume lorem ipsume lorem ipsume lorem ipsume
</div>

I simply apply the same logic using background-clip:text to color the text instead of the background:

.color {
  font-size: 1.5em;
  line-height: 1.5em;
  border: 2px solid;
  background: linear-gradient(red, red) left no-repeat;
  background-size: 0% 100%;
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  color: transparent;
  animation: change 5s linear forwards;
}

@keyframes change {
  100% {
    background-size: 100% 100%
  }
}

<span class="color">
 lorem ipsume lorem ipsume lorem ipsume lorem ipsume lorem ipsume lorem ipsume lorem ipsume lorem ipsume lorem ipsume 
</span>
<div class="color">
  lorem ipsume lorem ipsume lorem ipsume lorem ipsume lorem ipsume lorem ipsume lorem ipsume lorem ipsume lorem ipsume
</div>