sass: purge webkit-ism

it is 2020 and a blog for hackers should not use vendor prefix

Move SCSS partials to `/_sass/minimal-mistakes` for easier CSS customization

Merge branch 'release/3.3.7'

Merge branch 'release/3.0.0'

Merge branch 'feature/documentation-and-demo' into develop

Fix improperly positioned sticky element

Add subtle intro animation to elements and fix z-index stacking issues