fix: restore icon size workaround

packages/icon/src/vaadin-icon-font-size-mixin.d.ts

@@ -0,0 +1,16 @@
+/**
+ * @license
+ * Copyright (c) 2021 - 2025 Vaadin Ltd.
+ * This program is available under Apache License Version 2.0, available at https://vaadin.com/license/
+ */
+import type { Constructor } from '@open-wc/dedupe-mixin';
+
+/**
+ * Mixin which enables the font icon sizing fallback for browsers that do not support CSS Container Queries.
+ * The mixin does nothing if the browser supports CSS Container Query units for pseudo elements.
+ */
+export declare function IconFontSizeMixin<T extends Constructor<HTMLElement>>(
+  base: T,
+): Constructor<IconFontSizeMixinClass> & T;
+
+export declare class IconFontSizeMixinClass {}

packages/icon/src/vaadin-icon-font-size-mixin.js

@@ -0,0 +1,74 @@
+/**
+ * @license
+ * Copyright (c) 2021 - 2025 Vaadin Ltd.
+ * This program is available under Apache License Version 2.0, available at https://vaadin.com/license/
+ */
+import { ResizeMixin } from '@vaadin/component-base/src/resize-mixin.js';
+import { css, registerStyles } from '@vaadin/vaadin-themable-mixin/vaadin-themable-mixin.js';
+import { needsFontIconSizingFallback } from './vaadin-icon-helpers.js';
+
+const usesFontIconSizingFallback = needsFontIconSizingFallback();
+
+if (usesFontIconSizingFallback) {
+  registerStyles(
+    'vaadin-icon',
+    css`
+      :host::after,
+      :host::before {
+        font-size: var(--_vaadin-font-icon-size);
+      }
+    `,
+    'vaadin-icon-font-size-mixin-styles',
+  );
+}
+
+/**
+ * Mixin which enables the font icon sizing fallback for browsers that do not support CSS Container Queries.
+ * The mixin does nothing if the browser supports CSS Container Query units for pseudo elements.
+ *
+ * @polymerMixin
+ */
+export const IconFontSizeMixin = (superclass) =>
+  !usesFontIconSizingFallback
+    ? superclass
+    : class extends ResizeMixin(superclass) {
+        static get observers() {
+          return ['__iconFontSizeMixinfontChanged(iconClass, char, ligature)'];
+        }
+
+        /** @protected */
+        ready() {
+          super.ready();
+
+          // Update once initially to avoid a fouc
+          this.__updateFontIconSize();
+        }
+
+        /** @private */
+        __iconFontSizeMixinfontChanged(_iconClass, _char, _ligature) {
+          // Update when iconClass, char or ligature changes
+          this.__updateFontIconSize();
+        }
+
+        /**
+         * @protected
+         * @override
+         */
+        _onResize() {
+          // Update when the element is resized
+          this.__updateFontIconSize();
+        }
+
+        /**
+         * Updates the --_vaadin-font-icon-size CSS variable value if font icons are used.
+         *
+         * @private
+         */
+        __updateFontIconSize() {
+          if (this.char || this.iconClass || this.ligature) {
+            const { paddingTop, paddingBottom, height } = getComputedStyle(this);
+            const fontIconSize = parseFloat(height) - parseFloat(paddingTop) - parseFloat(paddingBottom);
+            this.style.setProperty('--_vaadin-font-icon-size', `${fontIconSize}px`);
+          }
+        }
+      };

packages/icon/src/vaadin-icon-helpers.js

@@ -0,0 +1,62 @@
+/**
+ * @license
+ * Copyright (c) 2016 - 2025 Vaadin Ltd.
+ * This program is available under Apache License Version 2.0, available at https://vaadin.com/license/
+ */
+
+import { isSafari } from '@vaadin/component-base/src/browser-utils.js';
+
+/**
+ * Checks if the current browser supports CSS Container Query units for pseudo elements.
+ * i.e. if the fix for https://bugs.webkit.org/show_bug.cgi?id=253939 is available.
+ */
+export function supportsCQUnitsForPseudoElements() {
+  const testStyle = document.createElement('style');
+  testStyle.textContent = `
+    .vaadin-icon-test-element {
+      container-type: size;
+      height: 2px;
+      visibility: hidden;
+      position: fixed;
+    }
+
+    .vaadin-icon-test-element::before {
+      content: '';
+      display: block;
+      height: 100cqh;
+    `;
+  const testElement = document.createElement('div');
+  testElement.classList.add('vaadin-icon-test-element');
+
+  const shadowParent = document.createElement('div');
+  shadowParent.attachShadow({ mode: 'open' });
+  shadowParent.shadowRoot.innerHTML = '<slot></slot>';
+  shadowParent.append(testElement.cloneNode());
+
+  document.body.append(testStyle, testElement, shadowParent);
+
+  const needsFallback = [...document.querySelectorAll('.vaadin-icon-test-element')].find(
+    (el) => getComputedStyle(el, '::before').height !== '2px',
+  );
+
+  testStyle.remove();
+  testElement.remove();
+  shadowParent.remove();
+  return !needsFallback;
+}
+
+/**
+ * Checks if the current browser needs a fallback for sizing font icons instead of relying on CSS Container Queries.
+ */
+export function needsFontIconSizingFallback() {
+  if (!CSS.supports('container-type: inline-size')) {
+    // The browser does not support CSS Container Queries at all.
+    return true;
+  }
+  if (!isSafari) {
+    // Browsers other than Safari support CSS Container Queries as expected.
+    return false;
+  }
+  // Check if the browser does not support CSS Container Query units for pseudo elements.
+  return !supportsCQUnitsForPseudoElements();
+}

packages/icon/src/vaadin-icon-mixin.d.ts

@@ -5,14 +5,15 @@
  */
 import type { Constructor } from '@open-wc/dedupe-mixin';
 import type { SlotStylesMixinClass } from '@vaadin/component-base/src/slot-styles-mixin.js';
+import type { IconFontSizeMixinClass } from './vaadin-icon-font-size-mixin.js';
 import type { IconSvgLiteral } from './vaadin-icon-svg.js';
 
 /**
  * A mixin providing common icon functionality.
  */
 export declare function IconMixin<T extends Constructor<HTMLElement>>(
   base: T,
-): Constructor<IconMixinClass> & Constructor<SlotStylesMixinClass> & T;
+): Constructor<IconFontSizeMixinClass> & Constructor<IconMixinClass> & Constructor<SlotStylesMixinClass> & T;
 
 export declare class IconMixinClass {
   /**

packages/icon/src/vaadin-icon-mixin.js

@@ -5,6 +5,7 @@
  */
 import { SlotStylesMixin } from '@vaadin/component-base/src/slot-styles-mixin.js';
 import { TooltipController } from '@vaadin/component-base/src/tooltip-controller.js';
+import { IconFontSizeMixin } from './vaadin-icon-font-size-mixin.js';
 import { unsafeSvgLiteral } from './vaadin-icon-svg.js';
 
 const srcCache = new Map();
@@ -14,9 +15,10 @@ const Iconset = customElements.get('vaadin-iconset');
 /**
  * @polymerMixin
  * @mixes SlotStylesMixin
+ * @mixes IconFontSizeMixin
  */
 export const IconMixin = (superClass) =>
-  class extends SlotStylesMixin(superClass) {
+  class extends IconFontSizeMixin(SlotStylesMixin(superClass)) {
     static get properties() {
       return {
         /**

packages/icon/test/icon-font.test.js

@@ -1,6 +1,7 @@
 import { expect } from '@vaadin/chai-plugins';
-import { fixtureSync, nextFrame, nextResize } from '@vaadin/testing-helpers';
+import { fixtureSync, isChrome, nextFrame, nextResize } from '@vaadin/testing-helpers';
 import '../src/vaadin-icon.js';
+import { needsFontIconSizingFallback, supportsCQUnitsForPseudoElements } from '../src/vaadin-icon-helpers.js';
 import { iconFontCss } from './test-icon-font.js';
 
 describe('vaadin-icon - icon fonts', () => {
@@ -267,4 +268,83 @@ describe('vaadin-icon - icon fonts', () => {
       expect(['"My icons 6"', 'My icons 6']).to.include(fontIconStyle.fontFamily);
     });
   });
+
+  // These tests make sure that the heavy container query fallback is only used
+  // when font icons are used.
+  describe('container query fallback', () => {
+    // Tests for browsers that require the fallback
+    const fallBackIt = needsFontIconSizingFallback() ? it : it.skip;
+    // Tests for browsers that we know for sure not to require the fallback
+    const supportedIt = isChrome ? it : it.skip;
+
+    let icon;
+
+    supportedIt('should support CQ width units on pseudo elements', () => {
+      expect(supportsCQUnitsForPseudoElements()).to.be.true;
+    });
+
+    supportedIt('should not need the fallback', () => {
+      expect(needsFontIconSizingFallback()).to.be.false;
+    });
+
+    fallBackIt('should not support CQ width units on pseudo elements', () => {
+      expect(supportsCQUnitsForPseudoElements()).to.be.false;
+    });
+
+    fallBackIt('should have the custom property (iconClass)', async () => {
+      icon = fixtureSync('<vaadin-icon icon-class="foo" style="--vaadin-icon-size: 24px"></vaadin-icon>');
+      await nextFrame();
+      expect(icon.style.getPropertyValue('--_vaadin-font-icon-size')).to.equal('24px');
+    });
+
+    fallBackIt('should have the custom property (char)', async () => {
+      icon = fixtureSync('<vaadin-icon char="foo" style="--vaadin-icon-size: 24px"></vaadin-icon>');
+      await nextFrame();
+      expect(icon.style.getPropertyValue('--_vaadin-font-icon-size')).to.equal('24px');
+    });
+
+    fallBackIt('should not have the custom property', async () => {
+      icon = fixtureSync('<vaadin-icon></vaadin-icon>');
+      await nextFrame();
+      expect(icon.style.getPropertyValue('--_vaadin-font-icon-size')).to.equal('');
+    });
+
+    fallBackIt('should set the custom property', async () => {
+      icon = fixtureSync('<vaadin-icon style="--vaadin-icon-size: 24px"></vaadin-icon>');
+      await nextFrame();
+      icon.iconClass = 'foo';
+      expect(icon.style.getPropertyValue('--_vaadin-font-icon-size')).to.equal('24px');
+    });
+
+    fallBackIt('should update the custom property', async () => {
+      icon = fixtureSync('<vaadin-icon icon-class="foo"></vaadin-icon>');
+      await nextFrame();
+      icon.style.width = '100px';
+      icon.style.height = '100px';
+      await nextResize(icon);
+      expect(icon.style.getPropertyValue('--_vaadin-font-icon-size')).to.equal('100px');
+    });
+
+    fallBackIt('should not update the custom property', async () => {
+      icon = fixtureSync('<vaadin-icon></vaadin-icon>');
+      await nextFrame();
+      icon.style.width = '100px';
+      icon.style.height = '100px';
+      await nextFrame(icon);
+      await nextFrame(icon);
+      expect(icon.style.getPropertyValue('--_vaadin-font-icon-size')).to.equal('');
+    });
+
+    fallBackIt('should have the same height as the host with shadow root', async () => {
+      const parent = fixtureSync('<div></div>');
+      parent.attachShadow({ mode: 'open' });
+      parent.shadowRoot.innerHTML = '<slot></slot>';
+
+      parent.append(icon);
+      await nextResize(icon);
+
+      const fontIconStyle = getComputedStyle(icon, ':before');
+      expect(parseInt(fontIconStyle.height)).to.be.closeTo(24, 1);
+    });
+  });
 });