Is there a way to see the stacking context, in IE/Firefox/Chrome/etc.?

For Chrome: the chrome 3d 'layer' tool does most of what you'd want I believe (similar to the other answer which is for MS Edge)

Find it in dev tools > overflow menu / 3 dots (hidden by default) > 'more tools' > 'layers'

https://www.youtube.com/watch?v=6je49J67TQk

If you use Chrome https://github.com/gwwar/z-context is a simple extension to see:

• If the current element creates a stacking context, and why
• What its parent stacking context is
• The z-index value

and important, like aprohl5 said: The z-index property can affect the stack order only if the position is explicitly set to fixed, absolute, or relative.

This is a nice way to mantain order with Sass https://www.smashingmagazine.com/2014/06/sassy-z-index-management-for-complex-layouts/

The current of MS Edge (using the Chromium engine with a build of "Beta", "Dev", or "Canary") now features: "Debug z-index stacking content with 3D View in the Microsoft Edge DevTools"

"a new feature to help debug z-index stacking context. The general 3D View shows a representation of the DOM (Document Object Model) depth using color and stacking, and the z-Index view helps you isolate the different stacking contexts of your page."

Press F12 (Windows), and then select the "3D tab" in the lower pane (may have to click "...") to view a visual representation.

More information: https://blogs.windows.com/msedgedev/2020/01/23/debug-z-index-3d-view-edge-devtools/

For Google Chrome and Firefox, I've created an open source extension that not only tells you if the element creates a z-index and why, but also shows a tree-like view of all stacking contexts in the page, and the stacking contexts that they're competing with regarding to the z-index value. You can see all these informations directly in the browser devtools, check out the github page for more info.

CSS stacking context inspector for Chrome

CSS stacking context inspector for Firefox