use imgui to make a simple dialogbox

// imgui - https://github.com/ocornut/imgui

auto& style = ImGui::GetStyle();
style.WindowPadding = {16, 16};
style.WindowRounding = 0.0f;
style.FramePadding = {4, 4};
style.FrameRounding = 0.0f;
style.ItemSpacing = {8, 4};
style.ItemInnerSpacing = {4, 4};
style.IndentSpacing = 16.0f;
style.ScrollbarSize = 12.0f;
style.ScrollbarRounding = 6.0f;
style.GrabMinSize = 36.0f;
style.GrabRounding = 6.0f;
style.WindowBorderSize = 1.0f;
style.ChildBorderSize = 1.0f;
style.PopupRounding = 2.0f;
style.FrameBorderSize = 1.0f;

ImGui::Begin("Hello, world!");
ImGui::Text("This is some useful text.");
ImGui::End();