How do I make a dockable window fill up the remaining dockspace programatically?

Question

I have a simple application with 2 dockable windows in a dockspace. One is sidebar and the other is the content.

I am using the docking branch of imgui

How do I make the content window fill up the remaining dockspace programmatically? Kind of like Visual Studio Code

Currently, there is some weird space between the sidebar and the content window

Current Output Expected Output, I got this by manually dragging the window and docking it

I do it like this

static ImGuiDockNodeFlags dockspace_flags = ImGuiDockNodeFlags_PassthruCentralNode;
ImGuiWindowFlags window_flags = ImGuiWindowFlags_NoDocking;

ImGuiViewport* viewport = ImGui::GetMainViewport();

ImGui::SetNextWindowPos(viewport->Pos);
ImGui::SetNextWindowSize(viewport->Size);
ImGui::SetNextWindowViewport(viewport->ID);

ImGui::PushStyleVar(ImGuiStyleVar_WindowRounding, 0.0f);
ImGui::PushStyleVar(ImGuiStyleVar_WindowBorderSize, 0.0f);
window_flags |= ImGuiWindowFlags_NoDecoration | ImGuiWindowFlags_NoMove;
window_flags |= ImGuiWindowFlags_NoBringToFrontOnFocus | ImGuiWindowFlags_NoNavFocus;

if (dockspace_flags & ImGuiDockNodeFlags_PassthruCentralNode)
    window_flags |= ImGuiWindowFlags_NoBackground;

ImGui::PushStyleVar(ImGuiStyleVar_WindowPadding, ImVec2(1.0f, 0.0f));
ImGui::Begin("Root", nullptr, window_flags);
ImGui::PopStyleVar();
ImGui::PopStyleVar(2);

// Dockspace
if (io.ConfigFlags & ImGuiConfigFlags_DockingEnable)
{
    ImGuiID dockspace_id = ImGui::GetID("Root");
    ImGui::DockSpace(dockspace_id, ImVec2(0.0f, 0.0f), dockspace_flags);
    
    static auto first_time = true;
    if (first_time)
    {
        first_time = false;
        
        ImGui::DockBuilderRemoveNode(dockspace_id);
        ImGui::DockBuilderAddNode(dockspace_id, dockspace_flags | ImGuiDockNodeFlags_DockSpace);
        ImGui::DockBuilderSetNodeSize(dockspace_id, viewport->Size);
        
        auto dock_id_left = ImGui::DockBuilderSplitNode(dockspace_id, ImGuiDir_Left, 0.2f, nullptr, &dockspace_id);
        auto dock_id_right = ImGui::DockBuilderSplitNode(dockspace_id, ImGuiDir_Right, 1.0f, nullptr, &dockspace_id);
        
        ImGui::DockBuilderDockWindow("Sidebar", dock_id_left);
        ImGui::DockBuilderDockWindow("Content", dock_id_right);
        ImGui::DockBuilderFinish(dockspace_id);
    }
}


ImGui::Begin("Sidebar");
ImGui::Text("Text 1");
ImGui::Text("Text 2");
ImGui::Text("Text 3");
ImGui::End();

ImGui::Begin("Content");
ImGui::Button("Button 1");
ImGui::Button("Button 2");
ImGui::Button("Button 3");
ImGui::End();