"position: fixed" not woking when parent has the "transform" CSS property - css

Question

In my project I have screen which should ease-in from right side of the screen so for that thing I have used transform: translateX(100%) and then changing that to transform: translateX(0%). it works fine I able to achieve the ease-in effect but in that screen I have action button which has css property of Position: Fixed;Bottom: 0px; but this is not working I mean its not sticking in the bottom of the screen.
Here is my JSfiddle : https://jsfiddle.net/sureshpattu/a1seze4x/
Html:
<header>
Heading
</header>
<div class="page__popup page__popup--ease-in-right page__action-btn--visible" style="height: 382px;">
<div class="container">
</div>
<button class="js-action-btn">
SELECT ROOMS
</button>
</div>
Css:
header {
background: #fff;
height: 60px;
position: fixed;
top: 0;
left: 0;
right: 0;
width: 100%;
z-index: 10;
box-shadow: 2px 2px 10px #000;
}
.container {
height: 382px;
}
.page__popup {
position: absolute;
top: 100vh;
z-index: 8;
display: block;
overflow-y: scroll;
max-height: 100vh;
width: 100%;
height: 0;
background: #ffffff;
.js-action-btn {
position: relative;
bottom: -50px;
transition: all 0.25s ease-in-out;
}
//Themes
&--ease-in-bottom {
&.visible {
transition: height 0.25s ease-in-out;
top: 54px;
right: 0;
bottom: 0;
left: 0;
}
}
&--ease-in-right {
transform: translateX(100%);
height: 100vh;
top: 60px;
&.visible {
transition: transform 0.25s ease-in-out;
transform: translateX(0);
}
}
}
.page__action-btn--visible {
.js-action-btn {
background: red;
width: 100%;
height: 30px;
position: fixed;
bottom: 0;
z-index: 10;
box-shadow: 0 7px 4px 10px rgba(0, 0, 0, .12);
}
}

Answer 1

This is not a bug.
Take a look at the spec: The Transform Rendering Model
Specifying a value other than ‘none’ for the ‘transform’ property
establishes a new local coordinate system at the element that it is
applied to.
So according to the spec: the element with fixed positioning will become relative to the element with the transform - not the viewport
As a workaround you could:
1) Use transitions (eg. on the left property) instead of transform (translateX)
2) Remove the position:fixed button from the container which uses transforms