FontChangerIssue

using System;
using System.IO;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Text.RegularExpressions;

namespace SteamFontChanger
{
    public partial class Form1 : Form
    {
        int newFont = 16;
        int prevFont;
        string line;
        string oldFont = "      font-size=";
        string filePath = "readme.txt";
        string startLine = "friends_chat_text";
        string fontLine = "     font-size=";
        string endLine = "friends_chat_accountid";
        string newFontS;

        public Form1()
        {
            InitializeComponent();
            System.IO.StreamReader prevFontRead = new System.IO.StreamReader("C:\\Users\\chris\\Desktop\\SteamFontSize\\prevfont.txt");
            prevFont = int.Parse(prevFontRead.ReadLine());
            oldFont = "     font-size=" + prevFont;
            prevLabel.Text = "Previous " + oldFont;
        }

        /// <summary>
        /// Edits the text in a file
        /// </summary>


    //v the below code
        private void editText()
        {
            System.IO.StreamReader read = new System.IO.StreamReader(filePath);
            StringBuilder write = new StringBuilder(filePath);

            while ((line = read.ReadLine()) != null)
            {
                if (startLine == read.ReadLine())
                {
                    while ((line = read.ReadLine()) != endLine)
                    {
                        write.Replace(oldFont, newFontS);
                    }
                }
            }
            MessageBox.Show("Done!");
        }
        // ^ the above code ^



        private void changeFont_Click(object sender, EventArgs e)
        {
            MessageBox.Show("If you have not done so, exit steam completely.");
            if (filePath != "readme.txt")
            {
                newFontS = fontLine + newFont.ToString();
                editText();
            }
            else
            {
                MessageBox.Show("Error: " + filePath + " is not a valid path, did you change the path?");
            }

        }

        private void textPath_TextChanged(object sender, EventArgs e)
        {
            filePath = textPath.Text + "\\steam\\resource\\styles\\steam.txt";
        }

        private void numericUpDown1_ValueChanged(object sender, EventArgs e)
        {
            //trying to get variable from box
            newFont = Convert.ToInt32(fontBox.Value);
        }
    }
}