Change button position in test subapp.

demo/DemoApp.tsx

@@ -479,12 +479,11 @@ export function DemoApp()
 					subapps.open(
 						<Subapp title={"Title test"}>
 							<p>A test content.</p>
-							<p>
-								Test button :
+							<Buttons placement={"center"}>
 								<Float mode={"click"} content={"Test content."}>
 									<button>A button with floating content</button>
 								</Float>
-							</p>
+							</Buttons>
 						</Subapp>
 					)
 				}}>Open a subapp