How to implement Youtube like preloader

I came across a pre-loader in YouTube, which look like this

I like to implement this type of preloader in my website, Couldn't find how to implement this type of preloader, It changes according to the Screen-size and theme[Dark or Normal]

I have implemented normal preloader like this

$(window).on('load', function () {
    $('#preloader').delay(350).fadeOut('slow');
    $('body').delay(350).css({ 'overflow': 'visible' });
})

Can anyone help to find the type of preloader used, Is is this image or something else.

Solution

These are called Skeletal loading preloaders, you may refer to this example also consider using this library for easily creating such preloaders.

.timeline-item {
    background: #fff;
    border: 1px solid;
    border-color: #e5e6e9 #dfe0e4 #d0d1d5;
    border-radius: 3px;
    padding: 12px;

    margin: 0 auto;
    max-width: 472px;
    min-height: 200px;
}

@keyframes placeHolderShimmer{
    0%{
        background-position: -468px 0
    }
    100%{
        background-position: 468px 0
    }
}

.animated-background {
    animation-duration: 1s;
    animation-fill-mode: forwards;
    animation-iteration-count: infinite;
    animation-name: placeHolderShimmer;
    animation-timing-function: linear;
    background: #f6f7f8;
    background: linear-gradient(to right, #eeeeee 8%, #dddddd 18%, #eeeeee 33%);
    background-size: 800px 104px;
    height: 96px;
    position: relative;
}

.background-masker {
    background: #fff;
    position: absolute;
}

/* Every thing below this is just positioning */

.background-masker.header-top,
.background-masker.header-bottom,
.background-masker.subheader-bottom {
    top: 0;
    left: 40px;
    right: 0;
    height: 10px;
}

.background-masker.header-left,
.background-masker.subheader-left,
.background-masker.header-right,
.background-masker.subheader-right {
    top: 10px;
    left: 40px;
    height: 8px;
    width: 10px;
}

.background-masker.header-bottom {
    top: 18px;
    height: 6px;
}

.background-masker.subheader-left,
.background-masker.subheader-right {
    top: 24px;
    height: 6px;
}


.background-masker.header-right,
.background-masker.subheader-right {
    width: auto;
    left: 300px;
    right: 0;
}

.background-masker.subheader-right {
    left: 230px;
}

.background-masker.subheader-bottom {
    top: 30px;
    height: 10px;
}

.background-masker.content-top,
.background-masker.content-second-line,
.background-masker.content-third-line,
.background-masker.content-second-end,
.background-masker.content-third-end,
.background-masker.content-first-end {
    top: 40px;
    left: 0;
    right: 0;
    height: 6px;
}

.background-masker.content-top {
    height:20px;
}

.background-masker.content-first-end,
.background-masker.content-second-end,
.background-masker.content-third-end{
    width: auto;
    left: 380px;
    right: 0;
    top: 60px;
    height: 8px;
}

.background-masker.content-second-line  {
    top: 68px;
}

.background-masker.content-second-end {
    left: 420px;
    top: 74px;
}

.background-masker.content-third-line {
    top: 82px;
}

.background-masker.content-third-end {
    left: 300px;
    top: 88px;
}

<div class="timeline-wrapper">
    <div class="timeline-item">
        <div class="animated-background">
            <div class="background-masker header-top"></div>
            <div class="background-masker header-left"></div>
            <div class="background-masker header-right"></div>
            <div class="background-masker header-bottom"></div>
            <div class="background-masker subheader-left"></div>
            <div class="background-masker subheader-right"></div>
            <div class="background-masker subheader-bottom"></div>
            <div class="background-masker content-top"></div>
            <div class="background-masker content-first-end"></div>
            <div class="background-masker content-second-line"></div>
            <div class="background-masker content-second-end"></div>
            <div class="background-masker content-third-line"></div>
            <div class="background-masker content-third-end"></div>
        </div>
    </div>
</div>