AngleSharp by Florian Rappl

CssOpacityProperty

sealed class CssOpacityProperty : CssProperty, ICssOpacityProperty, ICssProperty

Information can be found on MDN: https://developer.mozilla.org/en-US/docs/Web/CSS/opacity

public float Opacity { get; }

Gets the value that should be used for the opacity.

public void SetOpacity(float opacity)