C#

using System;
using System.Collections.Generic;
using System.Text;
using System.Windows.Forms;
using System.Runtime.InteropServices;
using System.Drawing;

class MyTextBox : TextBox {
  private const int WM_NCPAINT = 0x85;
  private const int WM_ERASEBKGND = 0x14;
  private const int WM_PAINT = 0xF;
  [DllImport("user32.dll")]
  static extern IntPtr GetDCEx(IntPtr hWnd, IntPtr hrgnClip, int flags);
  [DllImport("user32.dll")]
  static extern int ReleaseDC(IntPtr hWnd, IntPtr hDC);

  protected override void WndProc(ref Message message) {
    base.WndProc(ref message);
    if (message.Msg == WM_PAINT)
    {
      //get handle to a display device context
      IntPtr hdc = GetDCEx(message.HWnd, (IntPtr)1, 1 | 0x0020);

      if (hdc != IntPtr.Zero) {
        //get Graphics object from the display device context
        Graphics graphics = Graphics.FromHdc(hdc);
        Rectangle rectangle = new Rectangle(0, 0, Width, Height);
        ControlPaint.DrawBorder(graphics, rectangle, Color.White, ButtonBorderStyle.Solid);

        message.Result = (IntPtr)1;
        ReleaseDC(message.HWnd, hdc);
      }
    }
  }
}