Custom password protected pages

Hi All,
I am new to the forum and have made eight websites in the last year, all from self learning. However, I have come across a query that is needed for two recent sites.

I need to create a login area for frontend viewers to view certain individual pages. I know there is an option for this for each page in WordPress but the problem is that our institution blocks anyone outside of our network for logging into WordPress (I believe it is the wp-admin part that is blocked). This causes an issue with the regular password protection in WordPress so anyone outside the network cannot see password protected pages.

What I need is a plugin or CSS or anything really that I can add to certain pages. It doesn’t need to be complex, just a box to login with a fixed username and password. If there is anything better, I might need something for another site for registering to login to certain areas.

Note: these users are not to be entering the dashboard admin area, just viewing password protected pages. I have looked quite thoroughly and nothing is quite what I need.
Thanks for any advice,
Lee

The page I need help with: [log in to see the link]