void background()
{
ImGui::SetNextWindowPos(ImVec2(0, 0), ImGuiCond_Once);
ImGui::SetNextWindowSize(ImGui::GetIO().DisplaySize, ImGuiCond_Once);
ImGui::PushStyleColor(ImGuiCol_WindowBg, ImVec4(0.09f, 0.09f, 0.09f, 0.40f / 1.f * window_alpha));
static const auto flags = ImGuiWindowFlags_NoTitleBar | ImGuiWindowFlags_NoResize | ImGuiWindowFlags_NoMove | ImGuiWindowFlags_NoScrollbar | ImGuiWindowFlags_NoScrollWithMouse | ImGuiWindowFlags_NoBringToFrontOnFocus;
ImGui::Begin("##background", nullptr, flags);
ImGui::End();
ImGui::PopStyleColor();
}