why exactly do you want to hide the shell though? I assumed this was to stop students using the shell, for any reason. If it was for just hiding the shell from view by default, you could use one of those script executor browser extensions to close the shell when the repl loads up. Something like
javascript: document.querySelector("#main-content > div.css-1ye0645 > div > div.css-5o6owp > div:nth-child(5) > div.css-1iuoeqv > div.css-1wwkige > div > div.os-padding > div > div > div > div:nth-child(2) > div > div > button").click()