diff --git a/assets/styles/settings/_config.scss b/assets/styles/settings/_config.scss
index 4b9a401..02f8183 100644
--- a/assets/styles/settings/_config.scss
+++ b/assets/styles/settings/_config.scss
@@ -93,12 +93,16 @@ $to-colossal:   $from-colossal - 1 !default;
 // Z-indexes
 // =============================================================================
 
-$layers: (
-    "goku"     : 9000,
-    "loader"   : 500,
-    "modal"    : 300,
-    "header"   : 200,
-    "dropdown" : 100,
-    "default"  : 1,
-    "limbo"    : -999
+$z-indexes: (
+    "goku":       9000,
+    "transition": 500,
+    "toast":      400,
+    "popover":    300,
+    "modal":      250,
+    "sheet":      200,
+    "fixed":      150,
+    "sticky":     100,
+    "dropdown":   50,
+    "default":    1,
+    "limbo":      -999
 );
diff --git a/assets/styles/tools/_functions.scss b/assets/styles/tools/_functions.scss
index 35a8433..8853b2f 100644
--- a/assets/styles/tools/_functions.scss
+++ b/assets/styles/tools/_functions.scss
@@ -54,20 +54,29 @@
     @return ($size / $base) * 1rem;
 }
 
-// A function helper to avoid having to type `map-get($layers, ...)`
+// Retrieves the z-index from the {@see $layers master list}.
 //
 // @link on http://css-tricks.com/handling-z-index/
-// @param  {string} $layer The name of the z-index
-// @param  {number} $var   The modifier if needed
-// @return {number}        The corresponding z-index based on the $layers var
+//
+// @param  {string} $layer    The name of the z-index.
+// @param  {number} $modifier A positive or negative modifier to apply
+//     to the returned z-index value.
+// @throw  Error if the $layer does not exist.
+// @throw  Warning if the $modifier might overlap another master z-index.
+// @return {number}           The computed z-index of $layer and $modifier.
 
-@function z($layer, $var: 0) {
+@function z($layer, $modifier: 0) {
     @if not map-has-key($layers, $layer) {
-        @error "No z-index found in $layers map for `#{$layer}`. Property omitted.";
+        @error "Unknown master z-index layer: #{$layer}";
     }
 
-    $value: map-get($layers, $layer);
-    @return $value + $var;
+    @if ($modifier >= 50 or $modifier <= -50) {
+        @warn "Modifier may overlap the another master z-index layer: #{$modifier}";
+    }
+
+    $index: map-get($z-indexes, $layer);
+
+    @return $index + $modifier;
 }
 
 // Converts a number to a percentage.
@@ -110,7 +119,7 @@
 @function important($flag: false) {
     @if ($flag == true) {
         @return !important;
-    } @elseif ($important == false) {
+    } @else if ($important == false) {
         @return null;
     } @else {
         @error "`#{$flag}` needs to be `true` or `false`.";