Maximize Telegram Web so that large messages (like code samples, logs, or any kind of preformatted text) can be easily read (see screenshots below).
This extension only activity is to apply those 15 lines of CSS while visiting https://web.telegram.com.
Alternatively, you could install the very handy Custom Style Script extension and add those 15 lines of CSS, that's what I did at first, and the result is exactly the same, just less easy to install and share. Also, using a dedicated extension allows to mutualize the maintainance.