You have to keep the look and feel of all of your business’s branded web assets consistent with one another. It is wise to create a document that defines how this branding will continue to stabilize as your business offering change and as your staff (i.e. your graphic designer) turn over.
Related to this need, you might have heard of a “style guide.” Even in literary fields there are guides such as the MLA Handbook or the Chicago Manual of Style. There is something analogous to this in the web design world called a style guide, examples of which you can find on this post from Canva.
So What’s a Pattern Library?
A pattern library is great because it allows developers working with you to reuse code without having to slow down to make these types of decisions all on their own. MailChimp has theirs, a much more visually useful pattern library here:
If you are serious about UX, you will want to start collecting all of your code snippets, primarily from those pieces of your web assets that are the cleanest and most compatible with the other development tools you are using. Start organizing them, and create a living document that might change over time but at least will keep you on track as your business grows.