I give you some example code to know this better, here:
Code:
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>index</title>
<style type="text/css">
body{
font-size: 1.4em;
}
</style>
<script type="text/javascript">
alert('Hello, This is the Mistress.Ayin');
document.write("<b>Mistress.Ayin</b> grants you some knowledge !");
</script>
</head>
<body>
<h1>Welocome to <a href="https://f95zone.to/">F95zone</a> forum.</h1>
</body>
</html>
copy all of that codes in the text file, save that text file with this name "index.html" not the ".txt" suffix, a ".html" suffix, and open it with your browser in your computer, first you seen a popup, that popup window is a javascript code (this part "<b>Mistress.Ayin</b> grants you some knowledge", is an string in javascript combined with html too, because i make my name bold, this part is some similar of parser textify corruption of champion 2), runs before the html code, the style function is the css part, and inside the body type you seen the html code, in this simple code, i combined the javascript, css and html together. (of course i must to tell you, the programmer can code javascript in the separated file ".js", the css file ".css" and call them to inside of an "html" file, the electron frame work do that job too, it call that separated file "html", "js", "css" together inside of an empty chrome browser)
if you don't knows to make that code into a file, download this sample here.