Create custom window border disappears on resize

Pretty much what the title says.

I am trying to make my own border, for example visual studio 2015. Once the border is working for me, I have to add a child window which is the main window for my program, the border will be the parent. I will also try adding an outer glow as soon as I get it working.

But the problem im having right now is when I drag my border to resize to shrink it. Right or bottom start getting thinner depending on how fast I drag the mouse.

Is there a better way to do this or is there a simple step I can take to fix it.

#include <windows.h>

LPTSTR className_ = TEXT("BorderWindow");

BOOL WINAPI Init(HINSTANCE hInstance, INT cmdShow);
LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wparam, LPARAM lparam);


INT WINAPI wWinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPWSTR lpCmdLine, INT nCmdShow) {
    MSG msg;
    if (!Init(hInstance, nCmdShow)) {
        return FALSE;
    }

    while (GetMessage(&msg, NULL, 0, 0)) {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }

    return (INT)msg.wParam;
}


BOOL WINAPI Init(HINSTANCE hInstance, INT cmdShow)
{
    WNDCLASSEX wcex{ 0 };
    wcex.cbSize = sizeof(WNDCLASSEX);
    wcex.style = 0;
    wcex.lpfnWndProc = (WNDPROC)WndProc;
    wcex.hInstance = hInstance;
    wcex.hIcon = NULL;
    wcex.hCursor = LoadCursor(nullptr, IDC_ARROW);
    wcex.hbrBackground = (HBRUSH)(COLOR_HIGHLIGHT + 1);
    wcex.lpszClassName = className_;
    wcex.hIconSm = NULL;
    if (!RegisterClassEx(&wcex)) {
        return FALSE;
    }

    HWND hwnd_ = CreateWindow(className_, className_, WS_OVERLAPPEDWINDOW,
        CW_USEDEFAULT, 0, 200, 500, nullptr, nullptr, hInstance, nullptr);

    if (!hwnd_)
        return FALSE;

    ShowWindow(hwnd_, cmdShow);
    UpdateWindow(hwnd_);

    return TRUE;
}


void CreateHole(HWND hWnd)
{
    HRGN WindowRgn;
    HRGN HoleRgn;

    //Get the window region:
    RECT windowrect;
    GetWindowRect(hWnd, &windowrect);

    int width = windowrect.right - windowrect.left;
    int height = windowrect.bottom - windowrect.top;
    WindowRgn = CreateRectRgn(0, 0, width, height);

    //Create the hole region:
    HoleRgn = CreateRectRgn(2, 2, width - 2, height - 2);

    CombineRgn(WindowRgn, WindowRgn, HoleRgn, RGN_DIFF);
    SetWindowRgn(hWnd, WindowRgn, TRUE);
}


LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wparam, LPARAM lparam)
{
    switch (message)
    {
    case WM_DESTROY:
        PostQuitMessage(0);
        return 0;

    case WM_SIZE:
        CreateHole(hwnd);
        return 0;

    case WM_NCCALCSIZE:
        // remove default borders
        return 0;

    case WM_NCHITTEST:
    {
        RECT rc;
        GetClientRect(hwnd, &rc);
        POINT pt = { LOWORD(lparam), HIWORD(lparam) };
        ScreenToClient(hwnd, &pt);

        if (pt.y > (rc.bottom - 5))
        {
            if (pt.x > (rc.right - 5))
            {
                return HTBOTTOMRIGHT;
            }
        }

        return HTBORDER;
    }

    }
    return DefWindowProc(hwnd, message, wparam, lparam);
}