Tone and voice are two separate literary elements but for the purpose of saving time I’m defining and explaining both in the same post.
Tone is regarded as the attitude of the writer toward a subject or audience. The manor in which the writer approaches the common theme or subject matter is the tone. Tone can be conveyed through a writer’s choice of words, or perspective on a certain topic. The writer’s tone can be anything from happy, sad, sarcastic, silly, and/or any other attitude that can be named. I would suggest that you keep the tone of your novel appropriate for the assumed audience. For example, I try to keep my tone serious but light-hearted enough for my anticipated middle grade and young adult audience. I try to use words and phrases that are easily understood, which if you were writing a scientific thriller from the point of view of a scientist you might not want to do.
Voice is a more broad term and in some aspects can include tone in its definition. Voice refers to a writer’s individual style of writing, which can include how a writer paces their novel, develops characters, their syntax, dialogue, diction, and even punctuation. Voice may not just refer to one work by a writer but spans all of a writers works. Where as the tone of each piece of a writer’s work may be different, elements of their voice will be the same. If you would like examples of this you can read and compare my different posts.