Sounds like what you need is a style guide.
I've made a couple of these before (fair warning, it's a ton of work to make them correctly).
Personally, I use InDesign to put together documents like this. It gives you a lot of freedom with how you organize the content.
I've also seen a lot of brands publish theirs online. That makes sense if you have a ton of people in and out of the company who may need to access it.
As for a "how-to" on creating a style guide, I strongly encourage you to look up the style guides of big companies or any company you really like.
This link will take you to a section of one of Microsoft's style guides. Microsoft seems to split up their style guide depending on the application in question. If that makes sense for your company, you might consider doing the same.
More specific to developers
If you want the guide to be tailored to the developers, you might do something like Google has done here.
Their developer style guide is meant to help maintain a fairly consistent brand look and feel despite having countless devs in countless locations creating things for Google or in Google's style.
For example, in the Highlights section, Google talks about the tone that should be used in writing. Deeper into the guide, you'll see things like HTML formatting guidelines.
Whatever you end up doing, make sure you label the styles as guidelines unless it truly is a hard and fast rule (i.e. do not recolour the logo). I only say this because there's always going to be that case where the design works better a bit outside the original guidelines.
If you're worried about devs going way outside the correct style, add in conditions. For example, I always put in something like "If none of these colours are appropriate for your application, please consult the Marketing Team before choosing another colour."
Examples of more visual style guides/brand books
(btw also google "brand books")
You might do something like this for colour palettes.
Here's a great example for showing the style and size requirements for an element like a logo.