CSS animation, only render overlay on specific elements [duplicate]

Question

I have made this loading placeholder css animation. And on white bacground it looks correct because the animated/moving gradient is white with 20% opacity.

However sometimes the placeholder will be on a different coloured background and the the moving part also becomes visible on the background instead of just on the coloured darkened (which is undesired). please see snippet below:

.ph-item {
  position: relative;
  margin-bottom: 10px;
  overflow: hidden;
  border-radius: 2px;
}

.ph-item,
.ph-item *,
.ph-item ::after,
.ph-item ::before {
  box-sizing: border-box;
}

.ph-item::before {
  content: "";
  position: absolute;
  top: 0;
  right: 0;
  bottom: 0;
  left: 50%;
  z-index: 1;
  width: 500%;
  margin-left: -250%;
  animation: phAnimation 0.8s linear infinite;
  background: linear-gradient(to right, rgba(255, 255, 255, 0) 46%, rgba(255, 255, 255, 0.35) 50%, rgba(255, 255, 255, 0) 54%) 50% 50%;
}

.ph-item > * {
  padding-right: 10px;
}

.ph-row {
  margin-bottom: 5px;
}

.ph-row div {
  border-radius: 3px;
  height: 10px;
  background-color: rgba(0, 0, 0, 0.2);
}

.ph-row .standard,
.ph-row.big div {
  height: 20px;
  margin-right: 10px;
}


.ph-float-right {
  float: right;
  padding-left: 10px;
  margin-right: auto;
}

.ph-col-2 {
  width: 16.66667%;
  display: inline-block;
}

.ph-col-4 {
  width: 33.33333%;
  display: inline-block;
}

.ph-col-6 {
  width: 50%;
  display: inline-block;
}

.ph-col-8 {
  width: 66.66667%;
  display: inline-block;
}

.ph-col-10 {
  width: 83.33333%;
  display: inline-block;
}

.ph-col-12 {
  width: 100%;
  display: inline-block;
}

.ph-avatar {
  position: relative;
  width: 100%;
  min-width: 50px;
  background-color: rgba(0, 0, 0, 0.2);
  border-radius: 50%;
  overflow: hidden;
}

.ph-avatar::before {
  content: "";
  display: block;
  padding-top: 100%;
}

@keyframes phAnimation {
  0% {
    transform: translate3d(-30%, 0, 0);
  }

  100% {
    transform: translate3d(30%, 0, 0);
  }
}

<div style="width: 500px; height: 50px; background-color: darkblue; padding: 20px;">
  <div class="ph-item" style="max-width: 360px;">
    <div class="ph-col-2">
      <div class="ph-avatar"></div>
    </div>
    <div class="ph-col-10 ph-float-right">
      <div class="ph-row">
        <div class="ph-col-6 standard"></div>
        <div class="ph-col-10"></div>
      </div>
    </div>
  </div>
</div>
<div style="width: 500px; height: 50px; background-color: white; padding: 20px;">
  <div class="ph-item" style="max-width: 360px;">
    <div class="ph-col-2">
      <div class="ph-avatar"></div>
    </div>
    <div class="ph-col-10 ph-float-right">
      <div class="ph-row">
        <div class="ph-col-6 standard"></div>
        <div class="ph-col-10"></div>
      </div>
    </div>
  </div>
</div>

My question is, is it possible somehow to mask the animation to only be rendered on top of the darkened parts (ph-avatar and ph-col-xx) ?

And how is this achieved?

Answer 1

edit This is actually a duplicate of Background animation performance

Another approach could to use the after pseudo with the linear gradient reset with background-position. to keep each pseudo with coherent pieces of gradient, background-attachment will put things together. background-size will help also.

Demo of the idea below. CSS commented where updated or modified

.ph-item {
  position: relative;
  margin-bottom: 10px;
  overflow: hidden;
  border-radius: 2px;
}

.ph-item,
.ph-item *,
.ph-item ::after,
.ph-item ::before {
  box-sizing: border-box;
}
   /* selector removed 

.ph-item::before 

       and replaced by : */
.ph-avatar::after,
.ph-row .standard::after,
.ph-row .ph-col-10::after {
  content: "";
  position: absolute;
  top: 0;
  right: 0;
  bottom: 0;
  left: 50%;
  z-index: 1;
  width: 500%;
  margin-left: -250%;
  animation: phAnimation 2s linear infinite;/* duration to set to your needs */
  background: linear-gradient(
      to right,
      rgba(255, 255, 255, 0) 46%,
      rgba(255, 255, 255, 0.35) 50%,
      rgba(255, 255, 255, 0) 54%
    )
    50% 50% 
    rgba(0, 0, 0, 0.2);/* move here & added */
  background-attachment: fixed;/*  added */
  background-size: 1000px auto;/*  added */
}

.ph-item > * {
  padding-right: 10px;
}

.ph-row {
  margin-bottom: 5px;
}

.ph-row div {
  border-radius: 3px;
  height: 10px;
 /*background-color: rgba(0, 0, 0, 0.2); or move animation here from pseudo*/
}

.ph-row .standard,
.ph-row.big div {
  height: 20px;
  margin-right: 10px;
}

.ph-float-right {
  float: right;
  padding-left: 10px;
  margin-right: auto;
}

.ph-col-2 {
  width: 16.66667%;
  display: inline-block;
}

.ph-col-4 {
  width: 33.33333%;
  display: inline-block;
}

.ph-col-6 {
  width: 50%;
  display: inline-block;
  position: relative;/*  added */
  overflow: hidden;/*  added */
}

.ph-col-8 {
  width: 66.66667%;
  display: inline-block;
}

.ph-col-10 {
  width: 83.33333%;
  display: inline-block;
  position: relative;/*  added */
  overflow: hidden;/*  added */
}

.ph-col-12 {
  width: 100%;
  display: inline-block;
}

.ph-avatar {
  position: relative;
  width: 100%;
  min-width: 50px;
  border-radius: 50%;
  overflow: hidden;
}

.ph-avatar::before {
  content: "";
  display: block;
  padding-top: 100%;
}

@keyframes phAnimation {
  0% {
    background-position: -1000px 0;/*  modified */
  }

  100% {
    background-position: 1000px 0;/*  modified */
  }
}

<div style="width: 500px; height: 50px; background-color: darkblue; padding: 20px;">
  <div class="ph-item" style="max-width: 360px;">
    <div class="ph-col-2">
      <div class="ph-avatar"></div>
    </div>
    <div class="ph-col-10 ph-float-right">
      <div class="ph-row">
        <div class="ph-col-6 standard"></div>
        <div class="ph-col-10"></div>
      </div>
    </div>
  </div>
</div>
<div style="width: 500px; height: 50px; background-color: white; padding: 20px;">
  <div class="ph-item" style="max-width: 360px;">
    <div class="ph-col-2">
      <div class="ph-avatar"></div>
    </div>
    <div class="ph-col-10 ph-float-right">
      <div class="ph-row">
        <div class="ph-col-6 standard"></div>
        <div class="ph-col-10"></div>
      </div>
    </div>
  </div>
</div>
<div style="width: 500px; height: 50px; background-color: tomato; padding: 20px;">
  <div class="ph-item" style="max-width: 360px;">
    <div class="ph-col-2">
      <div class="ph-avatar"></div>
    </div>
    <div class="ph-col-10 ph-float-right">
      <div class="ph-row">
        <div class="ph-col-6 standard"></div>
        <div class="ph-col-10"></div>
      </div>
    </div>
  </div>
</div>
<div style="width: 500px; height: 50px; background-color: gold; padding: 20px;">
  <div class="ph-item" style="max-width: 360px;">
    <div class="ph-col-2">
      <div class="ph-avatar"></div>
    </div>
    <div class="ph-col-10 ph-float-right">
      <div class="ph-row">
        <div class="ph-col-6 standard"></div>
        <div class="ph-col-10"></div>
      </div>
    </div>
  </div>
</div>
<div style="width: 500px; height: 50px; background-color: purple; padding: 20px;">
  <div class="ph-item" style="max-width: 360px;">
    <div class="ph-col-2">
      <div class="ph-avatar"></div>
    </div>
    <div class="ph-col-10 ph-float-right">
      <div class="ph-row">
        <div class="ph-col-6 standard"></div>
        <div class="ph-col-10"></div>
      </div>
    </div>
  </div>
</div>
<div style="width: 500px; height: 50px; background-color: turquoise; padding: 20px;">
  <div class="ph-item" style="max-width: 360px;">
    <div class="ph-col-2">
      <div class="ph-avatar"></div>
    </div>
    <div class="ph-col-10 ph-float-right">
      <div class="ph-row">
        <div class="ph-col-6 standard"></div>
        <div class="ph-col-10"></div>
      </div>
    </div>
  </div>
</div>
<div style="width: 500px; height: 50px; background-color: gray; padding: 20px;">
  <div class="ph-item" style="max-width: 360px;">
    <div class="ph-col-2">
      <div class="ph-avatar"></div>
    </div>
    <div class="ph-col-10 ph-float-right">
      <div class="ph-row">
        <div class="ph-col-6 standard"></div>
        <div class="ph-col-10"></div>
      </div>
    </div>
  </div>
</div>
<div style="width: 500px; height: 50px; background-color: teal; padding: 20px;">
  <div class="ph-item" style="max-width: 360px;">
    <div class="ph-col-2">
      <div class="ph-avatar"></div>
    </div>
    <div class="ph-col-10 ph-float-right">
      <div class="ph-row">
        <div class="ph-col-6 standard"></div>
        <div class="ph-col-10"></div>
      </div>
    </div>
  </div>
</div>

Note , the background-animation can be set directly inside elements , pseudo are not necessary unless they have another purpose. possible option https://codepen.io/gc-nomade/pen/byJOJa