fix(button): activated outline button in toolbar no longer blends into background on MD dark mode (#29216)

Issue number: N/A

---------

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issue. -->

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etc). Submit multiple pull requests if needed. -->

## What is the current behavior?
<!-- Please describe the current behavior that you are modifying. -->

When using an outline-style button in a toolbar on `md` dark mode, the
activated style causes the button to become invisible.

Steps to repro in `main`:
1. Update the `css-variables` themes test to use the latest dark theme
styles (at least for v7) by replacing the contents of [this
file](https://github.com/ionic-team/ionic-framework/blob/main/core/src/themes/test/css-variables/css/dark.css)
with the [styles from the
docs](https://ionicframework.com/docs/theming/dark-mode#ionic-dark-theme).
2. Host the project locally and navigate to the test at
`themes/test/css-variables/index.html`.
3. Switch to dark mode within the page. Note that the activated outline
button isn't visible:

![image](https://github.com/ionic-team/ionic-framework/assets/90629384/fae1009f-4962-4e6b-b710-42deec083e84)


## What is the new behavior?
<!-- Please describe the behavior or changes that are being added by
this PR. -->

- Button styles corrected. The colors were correct for `ios` mode, but
had to be flipped for `md`, so I pulled the relevant styles into the
mode-specific stylesheets.
- CSS variables test has also been updated to use the same dark mode CSS
as in [the
docs](https://ionicframework.com/docs/theming/dark-mode#ionic-dark-theme),
as per the repro steps above. Let me know if you would rather this be
split into a separate PR.

Changes to the toolbar test were split into a separate PR to keep this
one clean and ensure the screenshot changes can be reviewed more
effectively: https://github.com/ionic-team/ionic-framework/pull/29231

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

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  5. Update the BREAKING.md file with the breaking change.
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See
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## Other information

<!-- Any other information that is important to this PR such as
screenshots of how the component looks before and after the change. -->

---------

Co-authored-by: ionitron <hi@ionicframework.com>

core/src/components/button/button.ios.scss

@@ -212,3 +212,12 @@
 :host(.button-solid.ion-color.ion-activated) .button-native::after {
   background: #{current-color(shade)};
 }
+
+
+// Activated Button in Toolbar
+// --------------------------------------------------
+
+:host(.button-outline.ion-activated.in-toolbar:not(.ion-color):not(.in-toolbar-color)) .button-native {
+  background: var(--ion-toolbar-color, var(--color));
+  color: #{var(--ion-toolbar-background, var(--background), ion-color(primary, contrast))};
+}

core/src/components/button/button.md.scss

@@ -160,3 +160,12 @@
     background: #{current-color(base)};
   }
 }
+
+
+// Activated Button in Toolbar
+// --------------------------------------------------
+
+:host(.button-outline.ion-activated.in-toolbar:not(.ion-color):not(.in-toolbar-color)) .button-native {
+  background: var(--ion-toolbar-background, var(--color));
+  color: #{var(--ion-toolbar-color, var(--background), ion-color(primary, contrast))};
+}

core/src/components/button/button.scss

@@ -331,11 +331,3 @@ ion-ripple-effect {
   background: #{var(--ion-toolbar-color, var(--background))};
   color: #{var(--ion-toolbar-background, var(--color))};
 }
-
-// Activated Button in Toolbar
-// --------------------------------------------------
-
-:host(.button-outline.ion-activated.in-toolbar:not(.ion-color):not(.in-toolbar-color)) .button-native {
-  background: var(--ion-toolbar-color, var(--color));
-  color: #{var(--ion-toolbar-background, var(--background), ion-color(primary, contrast))};
-}