Add menu styles.

examples/dom/gauge.cpp

@@ -0,0 +1,28 @@
+#include <chrono>
+#include <iostream>
+#include <thread>
+
+#include "ftxui/screen.hpp"
+#include "ftxui/dom/elements.hpp"
+
+int main(int argc, const char *argv[])
+{
+  for(float percentage = 0; percentage <= 1.0; percentage+=0.002) {
+    std::wstring data_downloaded =
+        std::to_wstring(int(percentage * 5000)) + L"/5000";
+    using namespace ftxui::dom;
+    auto document =
+        hbox(
+          text(L"downloading:"),
+          flex(gauge(percentage)),
+          text(L" " + data_downloaded)
+        );
+    auto screen = ftxui::Screen(100, 1);
+    Render(screen, document.get());
+    std::cout << '\r' << screen.ToString() << std::flush;
+
+    using namespace std::chrono_literals;
+    std::this_thread::sleep_for(0.01s);
+  }
+  std::cout << std::endl;
+}