LibWeb: Parse and store the opacity property

Author: https://github.com/Cleverking2003
Commit: 0e6ba6e1d3
Pull-request: https://github.com/SerenityOS/serenity/pull/8956
Reviewed-by: https://github.com/AtkinsSJ
Reviewed-by: https://github.com/alimpfard

Userland/Libraries/LibWeb/Layout/Node.cpp

@@ -327,6 +327,9 @@ void NodeWithStyle::apply_style(const CSS::StyleProperties& specified_style)
     computed_values.set_background_color(specified_style.color_or_fallback(CSS::PropertyID::BackgroundColor, document(), Color::Transparent));
 
     computed_values.set_z_index(specified_style.z_index());
+    computed_values.set_opacity(specified_style.opacity());
+    if (computed_values.opacity() == 0)
+        m_visible = false;
 
     if (auto width = specified_style.property(CSS::PropertyID::Width); width.has_value())
         m_has_definite_width = true;