root: viewport (default)
threshold: 0 (default)
intersectionRatio: 0
isIntersecting: false
root: this blue box
threshold: 0.5
intersectionRatio: 0
isIntersecting: false
root: this red box
rootMargin: -50px
threshold: [0, 0.25, 0.5, 0.75, 1]
intersectionRatio: 0
isIntersecting: false
root: <body>
threshold: [0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1]
intersectionRatio: 0
isIntersecting: false