LibWeb: Replace last couple of StyleValue casts with `as_foo()`

Userland/Libraries/LibWeb/CSS/Parser/Parser.cpp

@@ -2095,7 +2095,7 @@ RefPtr<StyleValue> Parser::parse_flex_value(ParsingContext const& context, Vecto
             return nullptr;
 
         // Zero is a valid value for basis, but only if grow and shrink are already specified.
-        if (value->is_numeric() && static_cast<NumericStyleValue&>(*value).value() == 0) {
+        if (value->has_number() && value->to_number() == 0) {
             if (flex_grow && flex_shrink && !flex_basis) {
                 flex_basis = LengthStyleValue::create(Length(0, Length::Type::Px));
                 continue;

Userland/Libraries/LibWeb/Layout/Node.cpp

@@ -220,7 +220,7 @@ void NodeWithStyle::apply_style(const CSS::StyleProperties& specified_style)
 
     auto bgimage = specified_style.property(CSS::PropertyID::BackgroundImage);
     if (bgimage.has_value() && bgimage.value()->is_image()) {
-        m_background_image = static_ptr_cast<CSS::ImageStyleValue>(bgimage.value());
+        m_background_image = bgimage.value()->as_image();
     }
 
     // FIXME: BorderXRadius properties are now BorderRadiusStyleValues, so make use of that.
@@ -374,7 +374,7 @@ void NodeWithStyle::apply_style(const CSS::StyleProperties& specified_style)
         // FIXME: Converting to pixels isn't really correct - values should be in "user units"
         //        https://svgwg.org/svg2-draft/coords.html#TermUserUnits
         if (stroke_width.value()->is_numeric())
-            computed_values.set_stroke_width(CSS::Length::make_px(static_cast<CSS::NumericStyleValue const&>(*stroke_width.value()).value()));
+            computed_values.set_stroke_width(CSS::Length::make_px(stroke_width.value()->to_number()));
         else
             computed_values.set_stroke_width(stroke_width.value()->to_length());
     }