Newsletter sign-up form with success message

Arranging the picture div with grid to automatically set itself to mobile view without the height of the picture div distorting it. also, the form validation is really challenging.

Arrangement of the form validation to display the error message and the orientation of the div to change automatically from desktop to mobile view without distorting or need to use some adjustment on media query to balance the mobile view. also, the screen size of less than 310px width isn't satisfying and I don't know how to perfect it.

Kindly let me know if my html, CSS and JavaScript followed best practices without any repetition or reuse of property anywhere and if the codes are neat and clean enough.