Add menu styles.

examples/dom/dbox.cpp

@@ -0,0 +1,31 @@
+#include "ftxui/screen.hpp"
+#include "ftxui/dom/elements.hpp"
+#include <iostream>
+
+int main(int argc, const char *argv[])
+{
+  using namespace ftxui::dom;
+  auto document =
+    dbox(
+      frame(
+        vbox(
+          text(L"line_1"),
+          text(L"line_2"),
+          text(L"line_3"),
+          text(L"line_4"),
+          text(L"line_5")
+        )
+      ),
+      center(
+        frame(
+          text(L"overlay")
+        )
+      )
+    );
+  auto screen = ftxui::Screen::TerminalOutput(document);
+  Render(screen, document.get());
+
+  std::cout << screen.ToString();
+
+  return 0;
+}