The .toast-container tries to use the z-index CSS variable, which is defined under .toast.
However, this variable is not accessible to the container. This change copies the variable to the spot where it can be used.
postcss-values-parser returns a syntax error when a negative value is
provided in a `calc` function after a CSS variable.
This is not an issue with Bootstrap itself, but a workaround to allow
projects using postcss-values-parser to keep upgrading and compiling
bootstrap
Ref: shellscape/postcss-values-parser#138, twbs/bootstrap#35033
Fix: #36851
* Add z-index for .toast-container
- Adds positioning and z-index to toast container so that it has a system-declared layer in relation to other components.
- Updates docs to use the class better
Fixes $34028
* Remove unnecessary z-index from docs examples
* Convert bulk of division to multiplication
* Use custom divide() function instead of Dart Sass math module for greater compatibility
* Apply suggestions from code review
* Fix functions
