public IEnumerable<CssRule> Rewrite(CssRule rule)
{
var declaration = rule.GetDeclaration("opacity");
if (declaration == null)
{
yield return rule;
yield break;
}
var value = declaration.Value as CssNumber;
if (value == null)
{
yield return rule;
yield break;
}
var index = rule.IndexOf(declaration);
// Add the filter before the standard
rule.Insert(index, new CssDeclaration("filter", $"alpha(opacity={value})"));
yield return rule;
}
