offset

Default	Type
undefined	(Number | String)[] | TypeCallback

Controls the starting point of certain parts of an animation.

The offset of the keyframe specified as a number between 0.0 and 1.0 inclusive or null. This is equivalent to specifying start and end states in percentages in CSS stylesheets using @keyframes. If this value is null or missing, the keyframe will be evenly spaced between adjacent keyframes.

Read more on MDN

animate(ASTRO_ESCAPED_LEFT_CURLY_BRACKET
    duration: 2000,
    opacity: [ 0, 0.9, 1 ],
    easing: [ 'ease-in', 'ease-out' ],

    offset: [ "from", 0.8 ], // Shorthand for [ 0, 0.8, 1 ]
    // or
    offset: [ 0, "80%", "to" ], // Shorthand for [ 0, 0.8, 1 ]
    // or
    offset: [ "0", "0.8", "to" ], // Shorthand for [ 0, 0.8, 1 ]
});