reformat appearance of wp-comments-post.php

My unfinished blog is here: https://www.elizabethdoidge.com/index2.html
I tried entering an invalid email address and a horrible looking screen appeared saying ‘Error:please enter valid email address’ and it just sat there with nothing to click on to send you back to put it right, apart from my browser’s back arrow. I can change the text but would like to either change the screen to something more friendly (pink flowers? – maybe not) with a redirect button, or have the message appear on the Comment form itself.
Also, I’d like to add a screen after the comment has been submitted to say thanks, and you comment will be displayed once I’ve moderated it at my leisure and asserted my right to condemn and delete your foul language.
Looked at several other blogs which all had the same nasty Error screen so I couldn’t plagiarise them. Please help (again).