这只是一个微小的窗体特效，但有时也会有画龙点睛之效。

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

namespace winForm
{
    public partial class Form1 : Form
    {
        #region 窗体边框阴影效果变量申明

        const int CS_DropSHADOW = 0x20000;
        const int GCL_STYLE = (-26);
        //声明Win32 API
        [DllImport("user32.dll", CharSet = CharSet.Auto)]
        public static extern int SetClassLong(IntPtr hwnd, int nIndex, int dwNewLong);
        [DllImport("user32.dll", CharSet = CharSet.Auto)]
        public static extern int GetClassLong_r(IntPtr hwnd, int nIndex);

        #endregion

        public Form1()
        {
            InitializeComponent();
            SetClassLong(this.Handle, GCL_STYLE, GetClassLong_r(this.Handle, GCL_STYLE) | CS_DropSHADOW); //API函数加载，实现窗体边框阴影效果
        }
    }
}