The widgets section ID is “widgets”. Here’s info for all the default Customizer sections/panels:
- Site Identity – title_tagline – 20
- Colors – colors – 40
- Header Image – header_image – 60
- Background Image – background_image – 80
- Navigation – nav – 100
- Widgets – widgets – 110
- Static Front Page – static_front_page – 120
- all others – default – 160