I tend to include Bootstrap into my projects so I take advantage of it's classes when writing forms.

Ideally I like having something to start from, Semantic UI providing in my experience the most flexible framework when combining different UI elements. When I need some control/widget that's not covered by the framework (did this for Bootstrap too) I build it in such a way that it fits with the way the framework works and feels as much as possible. I generally stick with the default theme of the UI framework unless a design is handed to me and try just to follow best practices for accessibility and keep it clean.

Tip for forms I found out that more often than not I prefer tooltips for displaying validation messages, because unless it's the most boring example, fields often end up in different widgets/tables/containers that are sensitive to positioning and size. So if you end up making custom forms in these kinds of requirements keep that in mind.

Astoundingly, implementing a framework, library or component won out over building controls from scratch. Comments agreed with included that it actually depends on what is required, and that it is useful to include tool tips on forms as a type of validation. Please keep building beautiful stylish UI :)

It depends of what I'm doing, when I need a specific design I don't use a framework 'cause it would probably be slower to deal with their styles. But if there's no need to do a specific design bootstrap or materialize is my way to go.

I tend to include bootstrap for components and then skin the heck out of it. I'm not a huge fan of their stylings but if offers a really nice starting point.