Drawing a rectangle on a rectangle with GDI

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C++

Win32

GDI

Warning: super noob alert so bear with me. :D

I've only just begun learning the Win32 API and started using the GDI, etc and already I'm having some difficulty understanding.

This is my code:

#include <windows.h>

char ClassName[] = "myWindowClass";
HBRUSH hOrange = CreateSolidBrush(RGB(255,180,0));
HBRUSH hRed = CreateSolidBrush(RGB(255,0,0));
HBRUSH hYellow = CreateSolidBrush(RGB(255,255,0));

LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam,LPARAM lParam);

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE previnstance, LPSTR lpcmdline, int ncmdshow)
{
    WNDCLASSEX wc;     
    MSG msg;

    wc.cbSize = sizeof(WNDCLASSEX);                     
    wc.style = 0;                                       
    wc.lpfnWndProc = WndProc;                           
    wc.cbClsExtra = 0;                                  
    wc.cbWndExtra = 0;                                  
    wc.hInstance = hInstance;                           
    wc.hIcon = LoadIcon(NULL, IDI_APPLICATION);         
    wc.hCursor = LoadCursor(NULL, IDC_ARROW);           
    wc.hbrBackground = hYellow;        
    wc.lpszMenuName = NULL;                             
    wc.lpszClassName = ClassName;                      
    wc.hIconSm = LoadIcon(NULL, IDI_APPLICATION);      

    if (RegisterClassEx(&wc) == 0)                  
    {
        MessageBox(NULL,                                
                   "Windows class failed to register",  
                   "Error",                             
                   MB_ICONEXCLAMATION | MB_OK);         
        return 0;
    }

    HWND MainWindow;             
    MainWindow = CreateWindowEx( 
        WS_EX_CLIENTEDGE,        
        ClassName,              
        "Rectangles",            
        WS_OVERLAPPEDWINDOW,    
        CW_USEDEFAULT,          
        CW_USEDEFAULT,          
        320,                     
        540,                     
        NULL,                    
        NULL,                    
        hInstance,               
        NULL);                   

    if (MainWindow == NULL)
    {
        MessageBox(NULL,
                   "Failed to create window";,
                   "Error",
                   MB_ICONEXCLAMATION | MB_OK);
        return 0;
    }

    ShowWindow(MainWindow, ncmdshow);
    UpdateWindow(MainWindow);

    while(GetMessage(&msg, NULL, 0, 0) > 0) 
    {
        TranslateMessage(&msg);    
        DispatchMessage(&msg);
    }
    return msg.wParam;
    return 0;
}


LRESULT CALLBACK WndProc(HWND hwnd,     
                         UINT msg,       
                         WPARAM wParam,
                         LPARAM lParam)
{
    RECT secondbackground;
    RECT titlebox;
    HDC hdc;

    switch(msg)                          
    {
    case WM_PAINT:
        hdc = GetDC(hwnd);
        SetRect(&secondbackground, 3, 3, 297, 495);
        FillRect(hdc, &secondbackground, hOrange);
        SetRect(&titlebox, 20, 20, 278,45);
        FillRect(hdc,&titlebox, hYellow);
        ReleaseDC(hwnd, hdc);
        break;
    case WM_CLOSE:                       
        DestroyWindow(hwnd);             
        break;
    case WM_DESTROY:                    
        PostQuitMessage(0);             
        break;
    default:
        return DefWindowProc(hwnd, msg, wParam, lParam);
    }
    return 0;
}

My issue is that when i draw that second rectangle, i want to draw it on top of the first, so i figured it was just the order in which they were drawn, but clearly i'm mistaken cause when i run this, the second yellow rectangle is oddly strobing on the screen. If someone would like to enlighten me on the correct way to draw rectangles, i would greatly appreciate it. Btw, if there are any other little mistakes or anything, this is pretty much my first WinApi program, so any knowledge would be greatly appreciated. :)