Is putting a modal in javascript html css the same as in electron js?

I am trying to make it so that when i press a button, a modal appears. However, I am having trouble as it is not working in my java script file functionality. I already got the html and css parts down, but I am unsure how to make the javascript work. I started to wonder if this electron js thing is different from the usual javascript thing.

Javascript:

const { app, BrowserWindow, Menu} = require('electron')
const path=require('path')
const url=require('url')

function createWindow () {
  // Create the browser window.
  const mainWin = new BrowserWindow({
    width: 800,
    height: 600,
    resizable:false,
    webPreferences: {
      nodeIntegration: true
    }
  })

  // and load the index.html of the app.
  mainWin.loadFile('index.html')


  // Open the DevTools.
        //win.webContents.openDevTools()

  var menu = Menu.buildFromTemplate([
      {
          label: "Menu",
          submenu: [
              {label: 'Exit',
                accelerator: process.platform == 'darwin' ? 'Command+Q' :
                'Ctrl+Q',
                click(){
                    app.quit();
                }
            }
          ]
      },
      {
          label: 'Classes',
          submenu: [
              {label: 'Add Classes'},
              {label: 'Manage Classes'}
          ]
      },
      {
          label: 'Reply Slips',
          submenu: [
              {label: 'Add Reply Slips'},
              {label: 'Manage Reply Slips'}
          ]
      }
  ])
  Menu.setApplicationMenu(menu);
}

// This method will be called when Electron has finished
// initialization and is ready to create browser windows.
// Some APIs can only be used after this event occurs.
app.whenReady().then(createWindow)

// Quit when all windows are closed.
app.on('window-all-closed', () => {
  // On macOS it is common for applications and their menu bar
  // to stay active until the user quits explicitly with Cmd + Q
  if (process.platform !== 'darwin') {
    app.quit()
  }
})

app.on('activate', () => {
  // On macOS it's common to re-create a window in the app when the
  // dock icon is clicked and there are no other windows open.
  if (BrowserWindow.getAllWindows().length === 0) {
    createWindow()
  }
})

// In this file you can include the rest of your app's specific main process
// code. You can also put them in separate files and require them here.