DOES IT EXIST SOMETHING LIKE A "BASE" ANIME ART STYLE?

yeah tho it depends on era

Each studio tends to have their own particular style or elements to their animation they become known for, and it's typical for manga adaptations to mimic the style of the manga, but there's definitely enough common stylistic trends you could work out a "base".

The more standardized something looks, the easier it is for multiple people to animate it and worry less about consistency/staying on-model. Model sheets do this, yes, but on the larger scale the "general anime" style does this for p much everyone working in the anime industry

here's a thing with some visual comparisons



This is probably the kinda thing you're noticing

There are some base styles according to the era, the studio and genre (shounen vs shoujo). There are a couple of anime that are somewhat unique in some ways (like no game no life, which looked kind of messy on purpose, or texhnolyze, Casshern Sins .. ..).
And Vagabond for manga, seriously, nobody knows how he did it - brush only.

I guess you can easily see how all shoujo manga/anime have even bigger puppy eyes, much more detailed/messy hair, big mouths/lips among other things. Just slightly different and usually a bit softer.

Pentagon got you covered on the era-thing, which should be the most noticeable.