this is our index.html file

<!DOCTYPE html>
<html manifest="index.appcache">
<body>
    <p>Content</p>
</body>
</html>

then we will create index.appcache file with below codes

CACHE MANIFEST
index.html

write those files that you want to be cached load index.html then go for offline mode and reload the tab

Note: The two files must be in the same folder in this example