feat(a11y): add dynamic font scaling (#28314)

Issue number: resolves #24638, resolves #18592

---------

<!-- Please do not submit updates to dependencies unless it fixes an
issue. -->

<!-- Please try to limit your pull request to one type (bugfix, feature,
etc). Submit multiple pull requests if needed. -->

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

Developers have requested that Ionic Framework support the dynamic type
feature on iOS for accessibility purposes. Ionic applications do not
respond to font scaling on iOS which can create inaccessible
applications particularly for users with low vision. Ionic apps on
Android devices currently support the Android equivalent due to
functionality in the Chromium webview.

Developers have also requested a way of adjusting the fonts in their
Ionic UI components consistently.

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

- Ionic components now use `rem` instead of `px` where appropriate. This
means devs can change the font size on `html` and the text in supported
Ionic components will scale up/down appropriately
- Add support for Dynamic Type on iOS (the iOS version of Dynamic Font
Scaling)

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

<!-- If this introduces a breaking change, please describe the impact
and migration path for existing applications below. -->


## 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: Maria Hutt <thetaPC@users.noreply.github.com>
Co-authored-by: Brandy Carney <brandyscarney@users.noreply.github.com>
Co-authored-by: Shawn Taylor <shawn@ionic.io>
Co-authored-by: ionitron <hi@ionicframework.com>
Co-authored-by: Sean Perkins <sean@ionic.io>
Co-authored-by: Sean Perkins <13732623+sean-perkins@users.noreply.github.com>
Co-authored-by: Amanda Johnston <90629384+amandaejohnston@users.noreply.github.com>

core/src/components/toast/test/a11y/toast.e2e.ts

@@ -5,7 +5,7 @@ import { configs, test } from '@utils/test/playwright';
 /**
  * This test does not check LTR vs RTL layouts
  */
-configs({ directions: ['ltr'] }).forEach(({ title, config }) => {
+configs({ directions: ['ltr'] }).forEach(({ title, screenshot, config }) => {
   test.describe(title('toast: a11y'), () => {
     test.beforeEach(async ({ page }) => {
       await page.goto(`/src/components/toast/test/a11y`, config);
@@ -53,4 +53,138 @@ configs({ directions: ['ltr'] }).forEach(({ title, config }) => {
       await expect(toastButton).toHaveAttribute('aria-label', 'close button');
     });
   });
+
+  test.describe(title('toast: font scaling'), () => {
+    test('should scale header text on larger font sizes', async ({ page }) => {
+      await page.setContent(
+        `
+        <style>
+          html {
+            font-size: 310%;
+          }
+        </style>
+
+        <ion-toast is-open="true" header="Testing" message="Hello world"></ion-toast>
+      `,
+        config
+      );
+
+      const toast = page.locator('ion-toast');
+
+      await expect(toast).toBeVisible();
+
+      const toastWrapper = toast.locator('.toast-wrapper');
+      await expect(toastWrapper).toHaveScreenshot(screenshot('toast-header-scale'));
+    });
+
+    test('should scale message text on larger font sizes', async ({ page }) => {
+      await page.setContent(
+        `
+        <style>
+          html {
+            font-size: 310%;
+          }
+        </style>
+
+        <ion-toast is-open="true" message="Hello world"></ion-toast>
+      `,
+        config
+      );
+
+      const toast = page.locator('ion-toast');
+
+      await expect(toast).toBeVisible();
+
+      const toastWrapper = toast.locator('.toast-wrapper');
+      await expect(toastWrapper).toHaveScreenshot(screenshot('toast-message-scale'));
+    });
+
+    test('should scale content icon on larger font sizes', async ({ page }) => {
+      await page.setContent(
+        `
+        <style>
+          html {
+            font-size: 310%;
+          }
+        </style>
+
+        <ion-toast is-open="true" message="Hello world" icon="alert"></ion-toast>
+      `,
+        config
+      );
+
+      const toast = page.locator('ion-toast');
+
+      await expect(toast).toBeVisible();
+
+      const toastWrapper = toast.locator('.toast-wrapper');
+      await expect(toastWrapper).toHaveScreenshot(screenshot('toast-icon-scale'));
+    });
+
+    test('should scale button text on larger font sizes', async ({ page }) => {
+      await page.setContent(
+        `
+        <style>
+          html {
+            font-size: 310%;
+          }
+        </style>
+
+        <ion-toast is-open="true" message="Hello world"></ion-toast>
+      `,
+        config
+      );
+
+      const toast = page.locator('ion-toast');
+
+      toast.evaluate((el: HTMLIonToastElement) => {
+        el.buttons = [
+          {
+            text: 'Cancel',
+          },
+        ];
+      });
+
+      await expect(toast).toBeVisible();
+
+      const toastWrapper = toast.locator('.toast-wrapper');
+      await expect(toastWrapper).toHaveScreenshot(screenshot('toast-buttons-scale'));
+    });
+
+    test('should scale buttons and icons on larger font sizes', async ({ page }) => {
+      await page.setContent(
+        `
+        <style>
+          html {
+            font-size: 310%;
+          }
+        </style>
+
+        <ion-toast is-open="true" message="Hello world"></ion-toast>
+      `,
+        config
+      );
+
+      const toast = page.locator('ion-toast');
+
+      toast.evaluate((el: HTMLIonToastElement) => {
+        el.buttons = [
+          {
+            text: 'Cancel',
+            icon: 'close',
+          },
+        ];
+      });
+
+      await expect(toast).toBeVisible();
+
+      /**
+       * Linux incorrectly clips the screenshot when capturing the toast container
+       * with the inset styling.
+       *
+       * We capture the entire toast container (entire page) to avoid this issue.
+       */
+      await expect(toast).toHaveScreenshot(screenshot('toast-buttons-icon-scale'));
+    });
+  });
 });

core/src/components/toast/toast.ios.scss

@@ -10,6 +10,7 @@
   --button-color: #{$toast-ios-button-color};
   --color: #{$toast-ios-title-color};
   --max-width: #{$toast-max-width};
+  --max-height: #{$toast-ios-max-height};
   --start: 10px;
   --end: 10px;
 
@@ -68,7 +69,7 @@
 .toast-button {
   @include padding($toast-ios-button-padding-top, $toast-ios-button-padding-end, $toast-ios-button-padding-bottom, $toast-ios-button-padding-start);
 
-  height: $toast-ios-button-min-height;
+  min-height: $toast-ios-button-min-height;
 
   transition: background-color, opacity 100ms linear;
 

core/src/components/toast/toast.ios.vars.scss

@@ -3,71 +3,81 @@
 // iOS Toast
 // --------------------------------------------------
 
+/// @prop - The maximum height of the toast
+/// The maximum height of an iOS notification
+/// scaled to 310% is 478px.
+$toast-ios-max-height: 478px;
+
 /// @prop - Background Color of the toast wrapper
-$toast-ios-background-color:                      $background-color-step-50 !default;
+$toast-ios-background-color: $background-color-step-50 !default;
 
 /// @prop - Background Color alpha of the toast wrapper when translucent
-$toast-ios-translucent-background-color-alpha:    .8 !default;
+$toast-ios-translucent-background-color-alpha: 0.8 !default;
 
 /// @prop - Background Color of the toast wrapper when translucent
-$toast-ios-translucent-background-color:          rgba($background-color-rgb, $toast-ios-translucent-background-color-alpha) !default;
+$toast-ios-translucent-background-color: rgba(
+  $background-color-rgb,
+  $toast-ios-translucent-background-color-alpha
+) !default;
 
 /// @prop - Border radius of the toast wrapper
-$toast-ios-border-radius:                         14px !default;
+$toast-ios-border-radius: 14px !default;
 
 /// @prop - Color of the toast title
-$toast-ios-title-color:                           $text-color-step-150 !default;
+$toast-ios-title-color: $text-color-step-150 !default;
 
 /// @prop - Font size of the toast title
-$toast-ios-header-font-weight:                    500 !default;
+$toast-ios-header-font-weight: 500 !default;
 
 /// @prop - Spacing between the header and the message
-$toast-ios-header-margin-bottom:                  2px !default;
+$toast-ios-header-margin-bottom: 2px !default;
 
 /// @prop - Font size of the toast title
-$toast-ios-content-font-size:                     14px !default;
+$toast-ios-content-font-size: dynamic-font-clamp(1, 14px, 3.1) !default;
 
 /// @prop - Padding top of the toast content
-$toast-ios-content-padding-top:                   15px !default;
+$toast-ios-content-padding-top: 15px !default;
 
 /// @prop - Padding end of the toast content
-$toast-ios-content-padding-end:                   $toast-ios-content-padding-top !default;
+$toast-ios-content-padding-end: $toast-ios-content-padding-top !default;
 
 /// @prop - Padding bottom of the toast content
-$toast-ios-content-padding-bottom:                $toast-ios-content-padding-top !default;
+$toast-ios-content-padding-bottom: $toast-ios-content-padding-top !default;
 
 /// @prop - Padding start of the toast content
-$toast-ios-content-padding-start:                 $toast-ios-content-padding-end !default;
+$toast-ios-content-padding-start: $toast-ios-content-padding-end !default;
 
-/// @prop - Color of the toast button	
-$toast-ios-button-color:                          #{ion-color(primary, base)} !default;
+/// @prop - Color of the toast button
+$toast-ios-button-color: #{ion-color(primary, base)} !default;
 
 /// @prop - Filter of the translucent toast
-$toast-ios-translucent-filter:                    saturate(180%) blur(20px) !default;
+$toast-ios-translucent-filter: saturate(180%) blur(20px) !default;
 
 /// @prop - Minimum height of the toast button
-$toast-ios-button-min-height:                     44px !default;
+$toast-ios-button-min-height: 44px !default;
 
 /// @prop - Padding top of the toast button
-$toast-ios-button-padding-top:                    10px !default;
+$toast-ios-button-padding-top: 10px !default;
 
 /// @prop - Padding end of the toast button
-$toast-ios-button-padding-end:                    15px !default;
+$toast-ios-button-padding-end: 15px !default;
 
 /// @prop - Padding bottom of the toast button
-$toast-ios-button-padding-bottom:                 $toast-ios-button-padding-top !default;
+$toast-ios-button-padding-bottom: $toast-ios-button-padding-top !default;
 
 /// @prop - Padding start of the toast button
-$toast-ios-button-padding-start:                  15px !default;
+$toast-ios-button-padding-start: 15px !default;
 
 /// @prop - Font size of the toast button
-$toast-ios-button-font-size:                      17px !default;
+/// Uses the same font size scaling rules as back button.
+/// Prioritizing the toast header and message over the button.
+$toast-ios-button-font-size: dynamic-font-clamp(1, 17px, 1.294) !default;
 
 /// @prop - Font size of the toast button
-$toast-ios-button-font-weight:                    500 !default;
+$toast-ios-button-font-weight: 500 !default;
 
 /// @prop - Background color alpha of the toast activated button
-$toast-ios-button-opacity-activated:              .4 !default;
+$toast-ios-button-opacity-activated: 0.4 !default;
 
 /// @prop - Background color of the toast button
-$toast-ios-button-background-color:               transparent !default;
+$toast-ios-button-background-color: transparent !default;

core/src/components/toast/toast.md.vars.scss

@@ -4,91 +4,92 @@
 // --------------------------------------------------
 
 /// @prop - Background of the toast
-$toast-md-background:                              $text-color-step-200 !default;
+$toast-md-background: $text-color-step-200 !default;
 
 /// @prop - Box shadow of the toast
-$toast-md-box-shadow:                              0 3px 5px -1px rgba(0, 0, 0, .2), 0 6px 10px 0 rgba(0, 0, 0, .14), 0 1px 18px 0 rgba(0, 0, 0, .12) !default;
+$toast-md-box-shadow: 0 3px 5px -1px rgba(0, 0, 0, 0.2), 0 6px 10px 0 rgba(0, 0, 0, 0.14),
+  0 1px 18px 0 rgba(0, 0, 0, 0.12) !default;
 
 /// @prop - Font size of the toast
-$toast-md-font-size:                               14px !default;
+$toast-md-font-size: dynamic-font(14px) !default;
 
 /// @prop - Color of the toast
-$toast-md-color:                                   $background-color-step-50 !default;
+$toast-md-color: $background-color-step-50 !default;
 
 /// @prop - Border radius of the toast wrapper
-$toast-md-border-radius:                           4px !default;
+$toast-md-border-radius: 4px !default;
 
 /// @prop - Font size of the toast message
-$toast-md-header-line-height:                      20px !default;
+$toast-md-header-line-height: dynamic-font(20px) !default;
 
 /// @prop - Font size of the toast message
-$toast-md-header-font-weight:                      500 !default;
+$toast-md-header-font-weight: 500 !default;
 
 /// @prop - Spacing between the header and the message
-$toast-md-header-margin-bottom:                    2px !default;
+$toast-md-header-margin-bottom: 2px !default;
 
 /// @prop - Font size of the toast message
-$toast-md-message-line-height:                     20px !default;
+$toast-md-message-line-height: dynamic-font(20px) !default;
 
 /// @prop - Padding top of the toast message
-$toast-md-content-padding-top:                     14px !default;
+$toast-md-content-padding-top: 14px !default;
 
 /// @prop - Padding end of the toast content
-$toast-md-content-padding-end:                     16px !default;
+$toast-md-content-padding-end: 16px !default;
 
 /// @prop - Padding bottom of the toast content
-$toast-md-content-padding-bottom:                  $toast-md-content-padding-top !default;
+$toast-md-content-padding-bottom: $toast-md-content-padding-top !default;
 
 /// @prop - Padding start of the toast content
-$toast-md-content-padding-start:                   $toast-md-content-padding-end !default;
+$toast-md-content-padding-start: $toast-md-content-padding-end !default;
 
 /// @prop - Padding top of the toast button
-$toast-md-button-padding-top:                      10px !default;
+$toast-md-button-padding-top: 10px !default;
 
 /// @prop - Padding end of the toast button
-$toast-md-button-padding-end:                      15px !default;
+$toast-md-button-padding-end: 15px !default;
 
 /// @prop - Padding bottom of the toast button
-$toast-md-button-padding-bottom:                   $toast-md-button-padding-top !default;
+$toast-md-button-padding-bottom: $toast-md-button-padding-top !default;
 
 /// @prop - Padding start of the toast button
-$toast-md-button-padding-start:                    15px !default;
+$toast-md-button-padding-start: 15px !default;
 
 /// @prop - Font size of the toast button
-$toast-md-button-font-size:                        14px !default;
+$toast-md-button-font-size: dynamic-font(14px) !default;
 
 /// @prop - Font weight of the toast button
-$toast-md-button-font-weight:                      500 !default;
+$toast-md-button-font-weight: 500 !default;
 
 /// @prop - Letter spacing of the toast button
-$toast-md-button-letter-spacing:                   0.84px !default;
+$toast-md-button-letter-spacing: 0.84px !default;
 
 /// @prop - Background color of the toast button
-$toast-md-button-background-color:                 transparent !default;
+$toast-md-button-background-color: transparent !default;
 
 /// @prop - Text transform of the toast button
-$toast-md-button-text-transform:                   uppercase !default;
+$toast-md-button-text-transform: uppercase !default;
 
 /// @prop - Opacity of the toast button background on hover
-$toast-md-button-opacity-hover:                    0.08 !default;
+$toast-md-button-opacity-hover: 0.08 !default;
 
 /// @prop - Background color of the toast button on hover
-$toast-md-button-background-color-hover:           ion-color(primary, base, $toast-md-button-opacity-hover) !default;
+$toast-md-button-background-color-hover: ion-color(primary, base, $toast-md-button-opacity-hover) !default;
 
 /// @prop - Text color of the cancel toast button
-$toast-md-button-cancel-text-color:                $background-color-step-100 !default;
+$toast-md-button-cancel-text-color: $background-color-step-100 !default;
 
 /// @prop - Background color of the cancel toast button on hover
-$toast-md-button-cancel-background-color-hover:    rgba($background-color-rgb, $toast-md-button-opacity-hover) !default;
+$toast-md-button-cancel-background-color-hover: rgba($background-color-rgb, $toast-md-button-opacity-hover) !default;
 
 /// @prop - Padding of the icon only toast button
-$toast-md-button-icon-only-padding:                9px !default;
+$toast-md-button-icon-only-padding: 9px !default;
 
 /// @prop - Width of the icon only toast button
-$toast-md-button-icon-only-width:                  36px !default;
+$toast-md-button-icon-only-width: 36px !default;
 
 /// @prop - Height of the icon only toast button
-$toast-md-button-icon-only-height:                 $toast-md-button-icon-only-width !default;
+$toast-md-button-icon-only-height: $toast-md-button-icon-only-width !default;
 
 /// @prop - Border radius of the icon only toast button
-$toast-md-button-icon-only-border-radius:          50% !default;
+$toast-md-button-icon-only-border-radius: 50% !default;

core/src/components/toast/toast.scss

@@ -128,6 +128,10 @@
   @include margin(null, null, null, 16px);
 }
 
+.toast-content {
+  min-width: 0;
+}
+
 .toast-message {
   flex: 1;
 
@@ -165,7 +169,6 @@
   align-items: center;
 }
 
-
 // Toast Button: Hover
 // --------------------------------------------------