LibWeb: Add EdgeStyleValue

This represents a single edge and offset, this will be needed for
the values of background-position-x/y.

Userland/Libraries/LibWeb/CSS/StyleValues/EdgeStyleValue.cpp

@@ -0,0 +1,30 @@
+/*
+ * Copyright (c) 2023, MacDue <macdue@dueutil.tech>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include "EdgeStyleValue.h"
+
+namespace Web::CSS {
+
+ErrorOr<String> EdgeStyleValue::to_string() const
+{
+    auto to_string = [](PositionEdge edge) {
+        switch (edge) {
+        case PositionEdge::Left:
+            return "left";
+        case PositionEdge::Right:
+            return "right";
+        case PositionEdge::Top:
+            return "top";
+        case PositionEdge::Bottom:
+            return "bottom";
+        }
+        VERIFY_NOT_REACHED();
+    };
+
+    return String::formatted("{} {}", to_string(m_properties.edge), TRY(m_properties.offset.to_string()));
+}
+
+}

Userland/Libraries/LibWeb/CSS/StyleValues/EdgeStyleValue.h

@@ -0,0 +1,44 @@
+/*
+ * Copyright (c) 2023, MacDue <macdue@dueutil.tech>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibWeb/CSS/Enums.h>
+#include <LibWeb/CSS/PercentageOr.h>
+#include <LibWeb/CSS/StyleValue.h>
+
+namespace Web::CSS {
+
+class EdgeStyleValue final : public StyleValueWithDefaultOperators<EdgeStyleValue> {
+public:
+    static ValueComparingNonnullRefPtr<EdgeStyleValue> create(PositionEdge edge, LengthPercentage const& offset)
+    {
+        return adopt_ref(*new EdgeStyleValue(edge, offset));
+    }
+    virtual ~EdgeStyleValue() override = default;
+
+    PositionEdge edge() const { return m_properties.edge; }
+    LengthPercentage const& offset() const { return m_properties.offset; }
+
+    virtual ErrorOr<String> to_string() const override;
+
+    bool properties_equal(EdgeStyleValue const& other) const { return m_properties == other.m_properties; }
+
+private:
+    EdgeStyleValue(PositionEdge edge, LengthPercentage const& offset)
+        : StyleValueWithDefaultOperators(Type::Edge)
+        , m_properties { .edge = edge, .offset = offset }
+    {
+    }
+
+    struct Properties {
+        PositionEdge edge;
+        LengthPercentage offset;
+        bool operator==(Properties const&) const = default;
+    } m_properties;
+};
+
+}