Thank you for your comments. Today there are alternatives to building a button in Prismic. You need to use either a Link field or a custom code field. And if you want to reuse it, you can do it with a Content Relationship field. Because not every button in a web app has the same behavior so by having the components available to build whatever you need is more flexible!
For example, you can create a Custom Type 'Button' with a Rich text field to which you can add labels and a Link field to add links to internal documents or external URLs. Or you can add the same Link field and then your Custom code field to add the HTML and className you want there.