Currently, `$toast-border-radius` uses the value of `.25rem`. This is inconsistent with other variables such as `$btn-border-radius` and `$input-border-radius`, which uses the "global" `$border-radius` variable.
$toast-background-color: rgba($white, .85) !default;
$toast-border-width: 1px !default;
$toast-border-color: rgba(0, 0, 0, .1) !default;
-$toast-border-radius: .25rem !default;
+$toast-border-radius: $border-radius !default;
$toast-box-shadow: 0 .25rem .75rem rgba($black, .1) !default;
$toast-header-color: $gray-600 !default;