Make Ribbon Appear Behind Rectangle - css

Question

I am trying to create a ribbon at the beginning of a rectangle. However, I cannot figure out how to make it appear BEHIND the rectangle.
Please see this codepen: http://codepen.io/gosusheep/pen/aOqOBy
The part for creating the ribbon and putting it behind the rectangle is here:
.rectangle::before{
content: "";
width: 0;
height: 0;
display: block;
position: absolute;
z-index: -1;
border-left: 25px solid transparent;
border-right: 25px solid $blue;
border-top: 25px solid $blue;
border-bottom: 25px solid $blue;
left: -30px;
top: 10%;
}
Even with position: absolute, and z-index: -1, it appears ON TOP of the div.
Can anyone help with this?

Answer 1

What is happening here is that apparently, the property transform: translateX(-50%); it's "overriding" in some way the z-index. My solution is just center rectangle otherwise, for example:
.rectangle{
margin: 0 auto;
}
DEMO

Answer 2

The reason for your problem is not because children cannot be positioned behind their parent but because you are using a transform on the parent. Using transforms affect the stacking context like mentioned in this answer by BoltClock.
One solution would be to avoid the transform totally and use left: calc(50% - 100px) instead to position the ribbon at the center (like in the below snippet). (50% - 100px) is used as the value because 100px is half of the box width (50% is the center point of the parent).
.rectangle {
width: 200px;
height: 50px;
background-color: #8080ff;
position: relative;
left: calc(50% - 100px); /* newly added */
border: 1px #6666ff solid;
}
ul {
list-style: none;
}
li {
display: inline;
}
li + li::before {
content: " | ";
}
.container {
width: 100%;
position: relative;
}
.rectangle {
width: 200px;
height: 50px;
background-color: #8080ff;
position: relative;
left: calc(50% - 100px); /* newly added */
border: 1px #6666ff solid;
}
.rectangle::before {
content: "";
width: 0;
height: 0;
display: block;
position: absolute;
z-index: -1;
border-left: 25px solid transparent;
border-right: 25px solid #8080ff;
border-top: 25px solid #8080ff;
border-bottom: 25px solid #8080ff;
left: -30px;
top: 10%;
}
<p>put a pipe between nav elements</p>
<nav>
<ul>
<li>banana</li>
<li>woof</li>
<li>quack</li>
</ul>
</nav>
<p>Ribbon on the end of a rectangle</p>
<div class='container'>
<div class='rectangle'></div>
</div>
If in case you can't use the above solution, then you could follow the approach described below.
Assuming you don't have any other use for the ::after pseudo-element, you could use that to create the rectangle and give it a z-index higher than the ::before pseudo-element to make it appear behind the rectangle.
/* Modified */
.rectangle {
width: 200px;
height: 50px;
position: relative;
left: 50%;
transform: translateX(-50%);
}
/* Added */
.rectangle::after {
content: "";
width: 100%;
height: 100%;
top: 0px;
left: 0px;
display: block;
position: absolute;
background-color: #8080ff;
border: 1px #6666ff solid;
z-index: -1;
}
.rectangle{
padding: 4px;
box-sizing: border-box;
}
Below is a sample snippet:
ul {
list-style: none;
}
li {
display: inline;
}
li + li::before {
content: " | ";
}
.container {
width: 100%;
position: relative;
}
.rectangle::before {
content: "";
width: 0;
height: 0;
display: block;
position: absolute;
z-index: -2;
border-left: 25px solid transparent;
border-right: 25px solid #8080ff;
border-top: 25px solid #8080ff;
border-bottom: 25px solid #8080ff;
left: -30px;
top: 10%;
}
/* Modified */
.rectangle {
width: 200px;
height: 50px;
position: relative;
left: 50%;
transform: translateX(-50%);
}
/* Added */
.rectangle::after {
content: "";
width: 100%;
height: 100%;
top: 0px;
left: 0px;
display: block;
position: absolute;
background-color: #8080ff;
border: 1px #6666ff solid;
z-index: -1;
}
.rectangle{
padding: 4px;
box-sizing: border-box;
}
<p>put a pipe between nav elements</p>
<nav>
<ul>
<li>banana</li>
<li>woof</li>
<li>quack</li>
</ul>
</nav>
<p>Ribbon on the end of a rectangle</p>
<div class='container'>
<div class='rectangle'>
Some content
</div>
</div>

Answer 3

Solution here, look closely at z-indexes and positions
.container{
position: relative;
width: 100%;
z-index: 1;
}
.rectangle{
width: 200px;
height: 50px;
background-color: $blue;
position: absolute;
left: 50%;
border: 1px darken($blue,5%) solid;
}
.rectangle::after{
content: "";
width: 0;
height: 0;
border-left: 25px solid transparent;
border-right: 25px solid $blue;
border-top: 25px solid $blue;
border-bottom: 25px solid $blue;
left: -30px;
top: 10px;
position: absolute;
z-index: -1;
}
And your codepen edited http://codepen.io/anon/pen/mJXeed working now