Add demo on styling grid with HasTheme

src/main/java/com/vaadin/flow/component/grid/Grid.java

@@ -109,6 +109,7 @@
 @HtmlImport("frontend://bower_components/vaadin-checkbox/src/vaadin-checkbox.html")
 @HtmlImport("frontend://flow-component-renderer.html")
 @JavaScript("frontend://gridConnector.js")
+
 public class Grid<T> extends Component
         implements HasDataProvider<T>, HasStyle, HasSize, Focusable<Grid<T>>,
         SortNotifier<Grid<T>, GridSortOrder<T>>, HasTheme {

src/test/java/com/vaadin/flow/component/grid/demo/GridView.java

@@ -369,6 +369,7 @@ protected void initView() {
         createDisabledGrid();
         createBasicTreeGridUsage();
         createLazyLoadingTreeGridUsage();
+        createGridWithStyling();
 
         addCard("Grid example model",
                 new Label("These objects are used in the examples above"));
@@ -1082,6 +1083,21 @@ private void createDisabledGrid() {
         addCard("Disabled grid", grid, div);
     }
 
+    private void createGridWithStyling() {
+        // begin-source-example
+        // source-example-heading: Grid with styling
+        Grid<Person> grid = new Grid<>();
+        List<Person> people = createItems(50);
+        grid.setItems(people);
+
+        grid.addColumn(Person::getName).setHeader("Name");
+        grid.addColumn(Person::getAge).setHeader("Age");
+        grid.addThemeNames("no-border", "no-row-borders", "row-stripes");
+        // end-source-example
+        grid.setId("basic-grid-with-style");
+        addCard("Grid with styling", grid);
+    }
+
     private Map<PersonWithLevel, List<PersonWithLevel>> childMap;
 
     private void createBasicTreeGridUsage() {

src/test/java/com/vaadin/flow/component/grid/it/GridViewIT.java

@@ -676,6 +676,18 @@ public void disabledGrid_itemsAreDisabled() {
                 button.isEnabled());
     }
 
+    @Test
+    public void gridWithStyling_correctThemeAttribute() {
+        openTabAndCheckForErrors("");
+        GridElement grid = $(GridElement.class).id("basic-grid-with-style");
+        scrollToElement(grid);
+        waitUntil(driver -> grid.getAllColumns().size() == 2);
+
+        Assert.assertEquals("Grid should have the correct theme attribute.",
+                grid.getAttribute("theme"),
+                "no-row-borders no-border row-stripes");
+    }
+
     private WebElement getCellContent(GridTHTDElement cell) {
         return (WebElement) executeScript(
                 "return arguments[0].firstElementChild.assignedNodes()[0].firstElementChild;",