Animate a skewed element in the skew angle in CSS - html

Question

So I'm doing this for some lines on my webpage.
#keyframes dropHeader {
0% {
height: 0px;
}
100% {
height: 100%;
}
}
.slant-decor {
left: 50%;
height: 100%;
position: fixed;
display: inline-flex;
animation-name: dropHeader;
animation-iteration-count: 1;
animation-timing-function: ease-out;
animation-duration: 0.6s;
}
.slant-decor:after {
width: 5px;
height: 100%;
background-color: rgba(0, 0, 0, 0.55);
content: "";
position: relative;
margin-left: -5px;
transform: skewX(-30deg);
display: inline-block;
}
.slant-decor div {
width: 19px;
height: 100%;
display: inline-block;
margin-left: -4px;
-ms-transform: skewX(-30deg); /* IE 9 */
-webkit-transform: skewX(-30deg); /* Safari */
transform: skewX(-30deg); /* Standard syntax */
}
.decor-orange {
background-color: orange;
}
.decor-red {
background-color: red;
}
.decor-green {
background-color: green;
}
<div class="slant-decor">
<div class="decor-red"></div>
<div class="decor-orange"></div>
<div class="decor-green"></div>
</div>
As of right now, the animation on .slant-decor works fine, however - as you can see, it causes a kind of a weird effect on the lines. What I'd like to achieve is that the animation follow the skew angle aswell, creating an effect where the lines would slide in from the top of the page, at the right angle. How could I achieve this?

Answer 1

If my understanding is correct, setting a transform-origin: right top would produce the effect that you are looking for. The default value for transform-origin is 50% 50% (the center-mid point of the element). When you animate the height, this point is constantly changing and hence creates that weird effect. If the transform-origin is set to a point that is fixed then that problem would be avoided.
#keyframes dropHeader {
0% {
height: 0px;
}
100% {
height: 100%;
}
}
.slant-decor {
left: 50%;
height: 300px;
position: fixed;
display: inline-flex;
animation-name: dropHeader;
animation-iteration-count: 1;
animation-timing-function: ease-out;
animation-duration: 0.6s;
}
.slant-decor:after {
width: 5px;
height: 100%;
background-color: rgba(0, 0, 0, 0.55);
content: "";
position: relative;
margin-left: -5px;
transform-origin: right top;
transform: skewX(-30deg);
display: inline-block;
}
.slant-decor div {
width: 19px;
height: 100%;
display: inline-block;
margin-left: -4px;
transform-origin: right top;
transform: skewX(-30deg);
}
.decor-orange {
background-color: orange;
}
.decor-red {
background-color: red;
}
.decor-green {
background-color: green;
}
<div class="slant-decor">
<div class="decor-red"></div>
<div class="decor-orange"></div>
<div class="decor-green"></div>
</div>