[html] z-index not working with position absolute

I opened the console (chrome\firefox) and ran the following lines:

$("body").append("<div id=\"popupFrame\" style=\"width:100%;height:100%;background-color:black;opacity:0.5;position:absolute;top:0;left:0;z-index:1;\" />");
$("body").append("<div id=\"popupContent\" style=\"width:200px;height:200px;z-index:1000;background-color:white;\" >dasdasdsadasdasdasdasdasd</div>");

The #popupContent should be above all but it's affected by the #popupFrame opacity.

The content is not contained in #popupFrame what makes this very weird.

The goal is to create firefox like alert box

I faced this issue a lot when using position: absolute;, I faced this issue by using position: relative in the child element. don't need to change position: absolute to relative, just need to add in the child element look into the beneath two examples:

let toggle = document.getElementById('toggle')

toggle.addEventListener("click", () => {
 toggle.classList.toggle('change');
})

.container {
  width: 60px;
  height: 22px;
  background: #333;
  border-radius: 20px;
  position: relative;
  cursor: pointer;

}

.change .slide {
  transform: translateX(33px);
}

.slide {
  transition: 0.5s;
  width: 20px;
  height: 20px;
  background: #fff;
  border-radius: 20px;
  margin: 2px 2px;
  z-index: 100;
}

.dot {
  width: 10px;
  height: 16px;
  background: red;
  position: absolute;
  top: 4px;
  right: 5px;
  z-index: 1;
}

<div class="container" id="toggle">
  <div class="slide"></div>
  <div class="dot"></div>
</div>

This's how it can be fixed using position relative:

let toggle = document.getElementById('toggle')

toggle.addEventListener("click", () => {
 toggle.classList.toggle('change');
})

.container {
  width: 60px;
  height: 22px;
  background: #333;
  border-radius: 20px;
  position: relative;
  cursor: pointer;

}

.change .slide {
  transform: translateX(33px);
}

.slide {
  transition: 0.5s;
  width: 20px;
  height: 20px;
  background: #fff;
  border-radius: 20px;
  margin: 2px 2px;
  z-index: 100;
  
  // Just add position relative;
  position: relative;
}

.dot {
  width: 10px;
  height: 16px;
  background: red;
  position: absolute;
  top: 4px;
  right: 5px;
  z-index: 1;
}

<div class="container" id="toggle">
  <div class="slide"></div>
  <div class="dot"></div>
</div>

Sandbox here

Old question but this answer might help someone.

If you are trying to display the contents of the container outside of the boundaries of the container, make sure that it doesn't have overflow:hidden, otherwise anything outside of it will be cut off.

z-index only applies to elements that have been given an explicit position. Add position:relative to #popupContent and you should be good to go.

Opacity changes the context of your z-index, as does the static positioning. Either add opacity to the element that doesn't have it or remove it from the element that does. You'll also have to either make both elements static positioned or specify relative or absolute position. Here's some background on contexts: http://philipwalton.com/articles/what-no-one-told-you-about-z-index/