If you’ve come across websites that uses 0, 1, 999, 99999, 9999999 as z-index values, then you’ve probably already guessed that the layers have been arbitrarily arranged and therefore poses the imminent headache of maintaining those websites in the future.

The way I manage layers is thru SCSS placeholders. Assuming I have a couple of layered components to deal with, I extend a placeholder with the same class name but prefixed with %layer-.

.nav{
// some properties
    @extend %layer-nav;
}
.dimmer{
    // some properties
    @extend %layer-dimmer;
}
.modal{
    // some properties
    @extend %layer-modal;
}

Then, in a separate SCSS partial called _layers.scss, I lay these placeholders down, each in a one-liner manner so I can easily glance over the layers and their corresponding values.

%layer-nav  { z-index: 10; }
%layer-dimmer   { z-index: 11; }
%layer-modal    { z-index: 12; }

I also don’t mind extending the placeholder in different components first before declaring them because the compiler shall indicate some errors which I use to easily encode them in the layers partial file later on.

And that’s pretty much it. Because z-index values are implemented as placeholders, we don’t need to constantly revisit components just to adjust the values. We also don’t have to put a lot of comments to note how one thing affects another. And most importantly, we don’t have to jump tens and hundreds (or even thousands) of units just to make sure a box appears on top!

It’s also worth noting that in this implementation of @extend, sharing the same placeholder across multiple components may not be the best idea because of the naming convention.[EDIT] You're better off using variables in this case, as pointed out in the comments below.

I hope you guys find this useful as I have. Let me know what you think or if there’s an even easier way, feel free to share. I’ll be sure to check it out.