fix: remove flex: 1 from scroller base styles to respect explicit height (#11373)

Since v25.0, setting an explicit height on vaadin-scroller inside a flex
container had no effect because flex: 1 on :host forced the scroller to
grow and fill available space. 

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: DiegoCardoso

packages/scroller/src/styles/vaadin-scroller-base-styles.js

@@ -17,7 +17,6 @@ export const scrollerStyles = css`
     display: block;
     overflow: auto;
     outline: none;
-    flex: 1;
     box-sizing: border-box;
     padding: var(--vaadin-scroller-padding-block) var(--vaadin-scroller-padding-inline);
   }

packages/scroller/test/scroller.test.js

@@ -148,6 +148,26 @@ describe('vaadin-scroller', () => {
     });
   });
 
+  describe('explicit height in flex container', () => {
+    let container;
+
+    beforeEach(async () => {
+      container = fixtureSync(`
+        <div style="display: flex; flex-direction: column; height: 500px;">
+          <vaadin-scroller style="height: 200px;">
+            <div>Content</div>
+          </vaadin-scroller>
+        </div>
+      `);
+      scroller = container.querySelector('vaadin-scroller');
+      await nextRender();
+    });
+
+    it('should respect explicit height when inside a flex container', () => {
+      expect(scroller.offsetHeight).to.equal(200);
+    });
+  });
+
   describe('full height content', () => {
     let container;