Adjust styling for notification raised when attempting to save a view-only notebook

[agriyakhetarpal]

Yeah, we could adjust the styling for the notification raised when a user tries to perform a save action on view-only notebooks.

Though orange/yellow is meant to symbolize danger so maybe not a bad choice? But surely there is some rounding and borders we could adjust.

Originally posted by @krassowski in #75 (comment)

[agriyakhetarpal]

Having checked this; I think the orange/yellow styling is nice as is, so the only modifications we need to do here are to make it have rounded corners (not sure how that plays with the orange/yellow bar on top) and change the font family to Inter.