diff --git a/Libraries/LibWeb/CSS/CSSStyleProperties.cpp b/Libraries/LibWeb/CSS/CSSStyleProperties.cpp
index 79f1e06557b..9807d2553a6 100644
--- a/Libraries/LibWeb/CSS/CSSStyleProperties.cpp
+++ b/Libraries/LibWeb/CSS/CSSStyleProperties.cpp
@@ -1005,6 +1005,10 @@ RefPtr<CSSStyleValue const> CSSStyleProperties::style_value_for_computed_propert
                     return used_values_for_grid_template_rows;
                 }
             }
+        } else if (property_id == PropertyID::ZIndex) {
+            if (auto z_index = layout_node.computed_values().z_index(); z_index.has_value()) {
+                return NumberStyleValue::create(z_index.value());
+            }
         }
 
         if (!property_is_shorthand(property_id))
diff --git a/Libraries/LibWeb/CSS/ComputedProperties.cpp b/Libraries/LibWeb/CSS/ComputedProperties.cpp
index 1e1d53a736b..5238e34bb23 100644
--- a/Libraries/LibWeb/CSS/ComputedProperties.cpp
+++ b/Libraries/LibWeb/CSS/ComputedProperties.cpp
@@ -332,14 +332,24 @@ Optional<int> ComputedProperties::z_index() const
     auto const& value = property(PropertyID::ZIndex);
     if (value.has_auto())
         return {};
-    if (value.is_integer()) {
-        // Clamp z-index to the range of a signed 32-bit integer for consistency with other engines.
-        auto integer = value.as_integer().integer();
-        if (integer >= NumericLimits<int>::max())
+
+    // Clamp z-index to the range of a signed 32-bit integer for consistency with other engines.
+    auto clamp = [](auto number) -> int {
+        if (number >= NumericLimits<int>::max())
             return NumericLimits<int>::max();
-        if (integer <= NumericLimits<int>::min())
+        if (number <= NumericLimits<int>::min())
             return NumericLimits<int>::min();
-        return static_cast<int>(integer);
+        return static_cast<int>(number);
+    };
+
+    if (value.is_integer()) {
+        return clamp(value.as_integer().integer());
+    }
+    if (value.is_calculated()) {
+        auto maybe_double = value.as_calculated().resolve_number({});
+        if (maybe_double.has_value()) {
+            return clamp(maybe_double.value());
+        }
     }
     return {};
 }
diff --git a/Tests/LibWeb/Text/expected/wpt-import/css/css-values/signs-abs-computed.txt b/Tests/LibWeb/Text/expected/wpt-import/css/css-values/signs-abs-computed.txt
index 3262891a2a4..f85e97f026b 100644
--- a/Tests/LibWeb/Text/expected/wpt-import/css/css-values/signs-abs-computed.txt
+++ b/Tests/LibWeb/Text/expected/wpt-import/css/css-values/signs-abs-computed.txt
@@ -2,8 +2,8 @@ Harness status: OK
 
 Found 233 tests
 
-148 Pass
-85 Fail
+174 Pass
+59 Fail
 Pass	abs(1) should be used-value-equivalent to 1
 Pass	sign(1) should be used-value-equivalent to 1
 Pass	abs(-1) should be used-value-equivalent to 1
@@ -95,22 +95,22 @@ Pass	calc(sign(0pc)) should be used-value-equivalent to 0
 Pass	clamp(-1, calc( 1 / sign(sign(0pc))), 1) should be used-value-equivalent to 1
 Pass	calc(sign(0pt)) should be used-value-equivalent to 0
 Pass	clamp(-1, calc( 1 / sign(sign(0pt))), 1) should be used-value-equivalent to 1
-Fail	calc(sign(0em)) should be used-value-equivalent to 0
-Fail	clamp(-1, calc( 1 / sign(sign(0em))), 1) should be used-value-equivalent to 1
-Fail	calc(sign(0ex)) should be used-value-equivalent to 0
-Fail	clamp(-1, calc( 1 / sign(sign(0ex))), 1) should be used-value-equivalent to 1
-Fail	calc(sign(0ch)) should be used-value-equivalent to 0
-Fail	clamp(-1, calc( 1 / sign(sign(0ch))), 1) should be used-value-equivalent to 1
-Fail	calc(sign(0rem)) should be used-value-equivalent to 0
-Fail	clamp(-1, calc( 1 / sign(sign(0rem))), 1) should be used-value-equivalent to 1
-Fail	calc(sign(0vh)) should be used-value-equivalent to 0
-Fail	clamp(-1, calc( 1 / sign(sign(0vh))), 1) should be used-value-equivalent to 1
-Fail	calc(sign(0vw)) should be used-value-equivalent to 0
-Fail	clamp(-1, calc( 1 / sign(sign(0vw))), 1) should be used-value-equivalent to 1
-Fail	calc(sign(0vmin)) should be used-value-equivalent to 0
-Fail	clamp(-1, calc( 1 / sign(sign(0vmin))), 1) should be used-value-equivalent to 1
-Fail	calc(sign(0vmax)) should be used-value-equivalent to 0
-Fail	clamp(-1, calc( 1 / sign(sign(0vmax))), 1) should be used-value-equivalent to 1
+Pass	calc(sign(0em)) should be used-value-equivalent to 0
+Pass	clamp(-1, calc( 1 / sign(sign(0em))), 1) should be used-value-equivalent to 1
+Pass	calc(sign(0ex)) should be used-value-equivalent to 0
+Pass	clamp(-1, calc( 1 / sign(sign(0ex))), 1) should be used-value-equivalent to 1
+Pass	calc(sign(0ch)) should be used-value-equivalent to 0
+Pass	clamp(-1, calc( 1 / sign(sign(0ch))), 1) should be used-value-equivalent to 1
+Pass	calc(sign(0rem)) should be used-value-equivalent to 0
+Pass	clamp(-1, calc( 1 / sign(sign(0rem))), 1) should be used-value-equivalent to 1
+Pass	calc(sign(0vh)) should be used-value-equivalent to 0
+Pass	clamp(-1, calc( 1 / sign(sign(0vh))), 1) should be used-value-equivalent to 1
+Pass	calc(sign(0vw)) should be used-value-equivalent to 0
+Pass	clamp(-1, calc( 1 / sign(sign(0vw))), 1) should be used-value-equivalent to 1
+Pass	calc(sign(0vmin)) should be used-value-equivalent to 0
+Pass	clamp(-1, calc( 1 / sign(sign(0vmin))), 1) should be used-value-equivalent to 1
+Pass	calc(sign(0vmax)) should be used-value-equivalent to 0
+Pass	clamp(-1, calc( 1 / sign(sign(0vmax))), 1) should be used-value-equivalent to 1
 Pass	calc(sign(-0px)) should be used-value-equivalent to 0
 Fail	clamp(-1, calc( 1 / sign(sign(-0px))), 1) should be used-value-equivalent to -1
 Pass	calc(sign(-0cm)) should be used-value-equivalent to 0
@@ -125,21 +125,21 @@ Pass	calc(sign(-0pc)) should be used-value-equivalent to 0
 Fail	clamp(-1, calc( 1 / sign(sign(-0pc))), 1) should be used-value-equivalent to -1
 Pass	calc(sign(-0pt)) should be used-value-equivalent to 0
 Fail	clamp(-1, calc( 1 / sign(sign(-0pt))), 1) should be used-value-equivalent to -1
-Fail	calc(sign(-0em)) should be used-value-equivalent to 0
+Pass	calc(sign(-0em)) should be used-value-equivalent to 0
 Fail	clamp(-1, calc( 1 / sign(sign(-0em))), 1) should be used-value-equivalent to -1
-Fail	calc(sign(-0ex)) should be used-value-equivalent to 0
+Pass	calc(sign(-0ex)) should be used-value-equivalent to 0
 Fail	clamp(-1, calc( 1 / sign(sign(-0ex))), 1) should be used-value-equivalent to -1
-Fail	calc(sign(-0ch)) should be used-value-equivalent to 0
+Pass	calc(sign(-0ch)) should be used-value-equivalent to 0
 Fail	clamp(-1, calc( 1 / sign(sign(-0ch))), 1) should be used-value-equivalent to -1
-Fail	calc(sign(-0rem)) should be used-value-equivalent to 0
+Pass	calc(sign(-0rem)) should be used-value-equivalent to 0
 Fail	clamp(-1, calc( 1 / sign(sign(-0rem))), 1) should be used-value-equivalent to -1
-Fail	calc(sign(-0vh)) should be used-value-equivalent to 0
+Pass	calc(sign(-0vh)) should be used-value-equivalent to 0
 Fail	clamp(-1, calc( 1 / sign(sign(-0vh))), 1) should be used-value-equivalent to -1
-Fail	calc(sign(-0vw)) should be used-value-equivalent to 0
+Pass	calc(sign(-0vw)) should be used-value-equivalent to 0
 Fail	clamp(-1, calc( 1 / sign(sign(-0vw))), 1) should be used-value-equivalent to -1
-Fail	calc(sign(-0vmin)) should be used-value-equivalent to 0
+Pass	calc(sign(-0vmin)) should be used-value-equivalent to 0
 Fail	clamp(-1, calc( 1 / sign(sign(-0vmin))), 1) should be used-value-equivalent to -1
-Fail	calc(sign(-0vmax)) should be used-value-equivalent to 0
+Pass	calc(sign(-0vmax)) should be used-value-equivalent to 0
 Fail	clamp(-1, calc( 1 / sign(sign(-0vmax))), 1) should be used-value-equivalent to -1
 Pass	calc(sign(0s)) should be used-value-equivalent to 0
 Pass	clamp(-1, calc( 1 / sign(sign(0s))), 1) should be used-value-equivalent to 1
@@ -207,14 +207,14 @@ Pass	abs(-1deg) should be used-value-equivalent to 1deg
 Pass	abs(-1grad) should be used-value-equivalent to 1grad
 Pass	abs(-1rad) should be used-value-equivalent to 1rad
 Pass	abs(-1turn) should be used-value-equivalent to 1turn
-Fail	sign(10px - 1em) should be used-value-equivalent to 0; fontSize=10px
+Pass	sign(10px - 1em) should be used-value-equivalent to 0; fontSize=10px
 Fail	sign(10px - 2em) should be used-value-equivalent to -1; fontSize=10px
 Pass	calc(sign(10%) * 100px) should be used-value-equivalent to 100px
 Fail	calc(2.5 - sign(41px - 2em) / 2) should be used-value-equivalent to 2
 Fail	calc(2.5 - sign(40px - 2em) / 2) should be used-value-equivalent to 2.5
 Fail	calc(2.5 - sign(39px - 2em) / 2) should be used-value-equivalent to 3
 Fail	calc(3 + sign(42px - 2em)) should be used-value-equivalent to 4
-Fail	calc(3 + sign(40px - 2em)) should be used-value-equivalent to 3
+Pass	calc(3 + sign(40px - 2em)) should be used-value-equivalent to 3
 Fail	calc(3 + sign(38px - 2em)) should be used-value-equivalent to 2
 Pass	calc(50px + 100px * sign(42px - 2em)) should be used-value-equivalent to 150px
 Pass	calc(50px + 100px * sign(40px - 2em)) should be used-value-equivalent to 50px