How Does `clip-path` Impact Element Stacking Order in CSS?

How Clip-Path Affects the Stacking Order of Elements in the DOM

Clip-path is a CSS property that creates a clipping region, defining which parts of an element's content are visible. However, it has an unexpected effect on the stacking order, placing elements later in the DOM beneath those with clip-path.

Cause of the Problem

This occurs because, according to the CSS specification, using non-zero clip-path values creates a stacking context. A stacking context is a three-dimensional space where elements are rendered and layered according to their z-index.

In the case of clip-path, the element with the clip-path is placed in a new stacking context, and subsequent elements without explicit positioning are rendered in the original stacking context. This means that elements with clip-path will overlap elements without explicit positioning even if they appear later in the DOM.

Fixing the Issue

To resolve this issue, you can explicitly set the position of the element with clip-path to "relative" or "absolute," which moves it to the new stacking context created by the clip-path. This will ensure that elements later in the DOM remain above the element with the clip-path.

Example

Consider the following CSS code:

header {
  background: #a00;
  clip-path: polygon(0 0, 100% 0, 100% calc(100% - 5em), 0 100%);
}

h1 {
  margin: 0;
  padding: 2em;
  font: 300%;
  color: white;
  text-align: center;
}

section {
  background: #ccc;
  padding-top:5em;
  margin-top:-5em;
}

img {
  margin-top: -10em;
}

Initially, the image is hidden behind the header due to the clip-path on the header. By setting "position: relative" on the image, it moves to the same stacking context as the header and appears above it:

img {
  margin-top: -10em;
  position: relative;
}

Conclusion

Using clip-path creates a stacking context that affects the stacking order of subsequent elements. To ensure correct layering, explicitly set the position of the element with the clip-path to "relative" or "absolute" or consider using other techniques to control element overlapping.

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