feat: add method to customize Dialog overlay ARIA role

vaadin-dialog-flow-parent/vaadin-dialog-flow/src/main/java/com/vaadin/flow/component/dialog/Dialog.java

@@ -126,6 +126,8 @@ public Dialog() {
             width = event.getWidth();
             height = event.getHeight();
         });
+
+        setOverlayRole("dialog");
     }
 
     /**
@@ -968,6 +970,28 @@ protected void onAttach(AttachEvent attachEvent) {
         registerClientCloseHandler();
     }
 
+    /**
+     * Sets the ARIA role for the overlay element, used by screen readers.
+     *
+     * @param role
+     *            the role to set
+     */
+    public void setOverlayRole(String role) {
+        Objects.requireNonNull(role, "Role cannot be null");
+
+        getElement().setProperty("overlayRole", role);
+    }
+
+    /**
+     * Gets the ARIA role for the overlay element, used by screen readers.
+     * Defaults to {@code dialog}.
+     *
+     * @return the role
+     */
+    public String getOverlayRole() {
+        return getElement().getProperty("overlayRole");
+    }
+
     /**
      * Set the {@code aria-label} attribute for assistive technologies like
      * screen readers. An {@code undefined} value for this property (the

vaadin-dialog-flow-parent/vaadin-dialog-flow/src/test/java/com/vaadin/flow/component/dialog/DialogTest.java

@@ -158,6 +158,31 @@ public void isModal_trueByDefault() {
                 !dialog.getElement().getProperty("modeless", false));
     }
 
+    @Test
+    public void getOverlayRole_defaultDialog() {
+        Dialog dialog = new Dialog();
+
+        Assert.assertEquals("dialog", dialog.getOverlayRole());
+        Assert.assertEquals("dialog",
+                dialog.getElement().getProperty("overlayRole"));
+    }
+
+    @Test
+    public void setOverlayRole_getOverlayRole() {
+        Dialog dialog = new Dialog();
+        dialog.setOverlayRole("alertdialog");
+
+        Assert.assertEquals("alertdialog", dialog.getOverlayRole());
+        Assert.assertEquals("alertdialog",
+                dialog.getElement().getProperty("overlayRole"));
+    }
+
+    @Test(expected = NullPointerException.class)
+    public void setOverlayRole_null_throws() {
+        Dialog dialog = new Dialog();
+        dialog.setOverlayRole(null);
+    }
+
     @Test
     public void setModal_dialogCanBeModeless() {
         Dialog dialog = new Dialog();