refactor: add missing no-padding variant to dialog base styles (#9843)

Author: web-padawan

packages/dialog/src/styles/vaadin-dialog-overlay-base-styles.js

@@ -64,6 +64,10 @@ export const dialogOverlayBase = css`
     padding: var(--vaadin-dialog-padding, var(--vaadin-padding));
   }
 
+  :host([theme~='no-padding']) [part='content'] {
+    padding: 0 !important;
+  }
+
   :host(:is([has-header], [has-title])) [part='content'] {
     padding-top: 0;
   }

packages/dialog/test/visual/base/dialog.test.js

@@ -74,4 +74,13 @@ describe('dialog', () => {
     await nextUpdate(element);
     await visualDiff(div, 'header-title-long-single-word');
   });
+
+  it('no-padding theme', async () => {
+    element.setAttribute('theme', 'no-padding');
+    const contentStyles = new CSSStyleSheet();
+    contentStyles.insertRule('vaadin-dialog::part(content) { padding: 20px; }');
+    document.adoptedStyleSheets = [contentStyles];
+    await nextUpdate(element);
+    await visualDiff(div, 'content-no-padding-theme');
+  });
 });