LibWeb: Use IdentifierStyleValue for CSS 'position'

Libraries/LibWeb/CSS/Parser/CSSParser.cpp

@@ -386,6 +386,16 @@ static Optional<CSS::ValueID> value_id_from_string(const String& string)
         return CSS::ValueID::VendorSpecificCenter;
     if (string.equals_ignoring_case("-libweb-link"))
         return CSS::ValueID::VendorSpecificLink;
+    if (string.equals_ignoring_case("static"))
+        return CSS::ValueID::Static;
+    if (string.equals_ignoring_case("relative"))
+        return CSS::ValueID::Relative;
+    if (string.equals_ignoring_case("absolute"))
+        return CSS::ValueID::Absolute;
+    if (string.equals_ignoring_case("fixed"))
+        return CSS::ValueID::Fixed;
+    if (string.equals_ignoring_case("sticky"))
+        return CSS::ValueID::Sticky;
     if (string.starts_with("-libweb-palette-", CaseSensitivity::CaseInsensitive))
         return value_id_for_palette_string(string.substring_view(16, string.length() - 16));
     return {};

Libraries/LibWeb/CSS/StyleProperties.cpp

@@ -225,20 +225,25 @@ Optional<int> StyleProperties::z_index() const
     return static_cast<int>(value.value()->to_length().raw_value());
 }
 
-CSS::Position StyleProperties::position() const
+Optional<CSS::Position> StyleProperties::position() const
 {
-    if (property(CSS::PropertyID::Position).has_value()) {
-        String position_string = string_or_fallback(CSS::PropertyID::Position, "static");
-        if (position_string == "relative")
-            return CSS::Position::Relative;
-        if (position_string == "absolute")
-            return CSS::Position::Absolute;
-        if (position_string == "sticky")
-            return CSS::Position::Sticky;
-        if (position_string == "fixed")
-            return CSS::Position::Fixed;
+    auto value = property(CSS::PropertyID::Position);
+    if (!value.has_value() || !value.value()->is_identifier())
+        return {};
+    switch (static_cast<const IdentifierStyleValue&>(*value.value()).id()) {
+    case CSS::ValueID::Static:
+        return CSS::Position::Static;
+    case CSS::ValueID::Relative:
+        return CSS::Position::Relative;
+    case CSS::ValueID::Absolute:
+        return CSS::Position::Absolute;
+    case CSS::ValueID::Fixed:
+        return CSS::Position::Fixed;
+    case CSS::ValueID::Sticky:
+        return CSS::Position::Sticky;
+    default:
+        return {};
     }
-    return CSS::Position::Static;
 }
 
 bool StyleProperties::operator==(const StyleProperties& other) const

Libraries/LibWeb/CSS/StyleProperties.h

@@ -79,7 +79,7 @@ public:
     bool operator==(const StyleProperties&) const;
     bool operator!=(const StyleProperties& other) const { return !(*this == other); }
 
-    CSS::Position position() const;
+    Optional<CSS::Position> position() const;
     Optional<int> z_index() const;
 
 private:

Libraries/LibWeb/CSS/StyleValue.h

@@ -117,6 +117,11 @@ enum class ValueID {
     XxLarge,
     XxSmall,
     XxxLarge,
+    Static,
+    Relative,
+    Absolute,
+    Fixed,
+    Sticky,
 };
 
 enum class Position {