TextBox Colored Border

How to change Textbox border color when user enters in to it
Step 1:
Open visual studio ->New project-> Window form application
Add textbox from toolbox to the form and write the  following code

Form1.cs

using System;

using System.Collections.Generic;

using System.ComponentModel;

using System.Data;

using System.Drawing;

using System.Linq;

using System.Text;

using System.Windows.Forms;

namespace textboxcolorborder

{

    public partial class Form1 : Form

    {

        bool focus = false;

        public Form1()

        {

            InitializeComponent();

           

        }

      

        private void Form1_Load(object sender, EventArgs e)

        {

          

        }

        private void textBox1_Enter(object sender, EventArgs e)

        {

            focus = true;

            this.Refresh();

        }

        private void textBox1_Leave(object sender, EventArgs e)

        {

            focus = false;

            this.Refresh();

        }

        private void Form1_Paint(object sender, PaintEventArgs e)

        {

            if (focus)

            {

                textBox1.BorderStyle = BorderStyle.None;

                Pen p = new Pen(Color.Red);

                Graphics g = e.Graphics;

                int variance = 3;

                g.DrawRectangle(p, new Rectangle(textBox1.Location.X - variance, textBox1.Location.Y - variance, textBox1.Width + variance, textBox1.Height + variance));

            }

            else

            {

                textBox1.BorderStyle = BorderStyle.FixedSingle;

            }

        }

       

    }

}

 

Demo: