diff --git a/Libraries/LibWeb/CSS/StyleValues/ShorthandStyleValue.cpp b/Libraries/LibWeb/CSS/StyleValues/ShorthandStyleValue.cpp
index 82c55bc651f..aebecf686ab 100644
--- a/Libraries/LibWeb/CSS/StyleValues/ShorthandStyleValue.cpp
+++ b/Libraries/LibWeb/CSS/StyleValues/ShorthandStyleValue.cpp
@@ -279,6 +279,13 @@ String ShorthandStyleValue::to_string(SerializationMode mode) const
             return "normal"_string;
         return MUST(String::join(' ', values));
     }
+    case PropertyID::Gap: {
+        auto row_gap = longhand(PropertyID::RowGap);
+        auto column_gap = longhand(PropertyID::ColumnGap);
+        if (row_gap == column_gap)
+            return row_gap->to_string(mode);
+        return MUST(String::formatted("{} {}", row_gap->to_string(mode), column_gap->to_string(mode)));
+    }
     case PropertyID::GridArea: {
         auto& row_start = longhand(PropertyID::GridRowStart)->as_grid_track_placement();
         auto& column_start = longhand(PropertyID::GridColumnStart)->as_grid_track_placement();
@@ -411,13 +418,21 @@ String ShorthandStyleValue::to_string(SerializationMode mode) const
 
         StringBuilder builder;
         auto first = true;
-        for (auto& value : m_properties.values) {
+        for (size_t i = 0; i < m_properties.values.size(); ++i) {
+            auto value = m_properties.values[i];
+            auto value_string = value->to_string(mode);
+            auto initial_value_string = property_initial_value(m_properties.sub_properties[i])->to_string(mode);
+            if (value_string == initial_value_string)
+                continue;
             if (first)
                 first = false;
             else
                 builder.append(' ');
             builder.append(value->to_string(mode));
         }
+        if (builder.is_empty())
+            return m_properties.values.first()->to_string(mode);
+
         return MUST(builder.to_string());
     }
 }
diff --git a/Tests/LibWeb/Text/expected/css/CSSStyleProperties-all-supported-properties-and-default-values.txt b/Tests/LibWeb/Text/expected/css/CSSStyleProperties-all-supported-properties-and-default-values.txt
index d45264ddd73..17783855037 100644
--- a/Tests/LibWeb/Text/expected/css/CSSStyleProperties-all-supported-properties-and-default-values.txt
+++ b/Tests/LibWeb/Text/expected/css/CSSStyleProperties-all-supported-properties-and-default-values.txt
@@ -9,9 +9,9 @@ All supported properties and their default values exposed from CSSStylePropertie
 'WebkitAlignSelf': 'auto'
 'webkitAlignSelf': 'auto'
 '-webkit-align-self': 'auto'
-'WebkitAnimation': 'none 0s ease 1 normal running 0s none'
-'webkitAnimation': 'none 0s ease 1 normal running 0s none'
-'-webkit-animation': 'none 0s ease 1 normal running 0s none'
+'WebkitAnimation': 'none'
+'webkitAnimation': 'none'
+'-webkit-animation': 'none'
 'WebkitAnimationDelay': '0s'
 'webkitAnimationDelay': '0s'
 '-webkit-animation-delay': '0s'
@@ -111,9 +111,9 @@ All supported properties and their default values exposed from CSSStylePropertie
 'WebkitTransformOrigin': '50% 50%'
 'webkitTransformOrigin': '50% 50%'
 '-webkit-transform-origin': '50% 50%'
-'WebkitTransition': 'all 0s ease 0s'
-'webkitTransition': 'all 0s ease 0s'
-'-webkit-transition': 'all 0s ease 0s'
+'WebkitTransition': 'all'
+'webkitTransition': 'all'
+'-webkit-transition': 'all'
 'WebkitTransitionDelay': '0s'
 'webkitTransitionDelay': '0s'
 '-webkit-transition-delay': '0s'
@@ -137,7 +137,7 @@ All supported properties and their default values exposed from CSSStylePropertie
 'align-items': 'normal'
 'alignSelf': 'auto'
 'align-self': 'auto'
-'animation': 'none 0s ease 1 normal running 0s none'
+'animation': 'none'
 'animationDelay': '0s'
 'animation-delay': '0s'
 'animationDirection': 'normal'
@@ -184,25 +184,25 @@ All supported properties and their default values exposed from CSSStylePropertie
 'background-size': 'auto auto'
 'blockSize': '0px'
 'block-size': '0px'
-'border': '0px none rgb(0, 0, 0)'
-'borderBlockEnd': 'medium none rgb(0, 0, 0)'
-'border-block-end': 'medium none rgb(0, 0, 0)'
+'border': '0px rgb(0, 0, 0)'
+'borderBlockEnd': 'rgb(0, 0, 0)'
+'border-block-end': 'rgb(0, 0, 0)'
 'borderBlockEndColor': 'rgb(0, 0, 0)'
 'border-block-end-color': 'rgb(0, 0, 0)'
 'borderBlockEndStyle': 'none'
 'border-block-end-style': 'none'
 'borderBlockEndWidth': 'medium'
 'border-block-end-width': 'medium'
-'borderBlockStart': 'medium none rgb(0, 0, 0)'
-'border-block-start': 'medium none rgb(0, 0, 0)'
+'borderBlockStart': 'rgb(0, 0, 0)'
+'border-block-start': 'rgb(0, 0, 0)'
 'borderBlockStartColor': 'rgb(0, 0, 0)'
 'border-block-start-color': 'rgb(0, 0, 0)'
 'borderBlockStartStyle': 'none'
 'border-block-start-style': 'none'
 'borderBlockStartWidth': 'medium'
 'border-block-start-width': 'medium'
-'borderBottom': '0px none rgb(0, 0, 0)'
-'border-bottom': '0px none rgb(0, 0, 0)'
+'borderBottom': '0px rgb(0, 0, 0)'
+'border-bottom': '0px rgb(0, 0, 0)'
 'borderBottomColor': 'rgb(0, 0, 0)'
 'border-bottom-color': 'rgb(0, 0, 0)'
 'borderBottomLeftRadius': '0px'
@@ -217,24 +217,24 @@ All supported properties and their default values exposed from CSSStylePropertie
 'border-collapse': 'separate'
 'borderColor': 'rgb(0, 0, 0)'
 'border-color': 'rgb(0, 0, 0)'
-'borderInlineEnd': 'medium none rgb(0, 0, 0)'
-'border-inline-end': 'medium none rgb(0, 0, 0)'
+'borderInlineEnd': 'rgb(0, 0, 0)'
+'border-inline-end': 'rgb(0, 0, 0)'
 'borderInlineEndColor': 'rgb(0, 0, 0)'
 'border-inline-end-color': 'rgb(0, 0, 0)'
 'borderInlineEndStyle': 'none'
 'border-inline-end-style': 'none'
 'borderInlineEndWidth': 'medium'
 'border-inline-end-width': 'medium'
-'borderInlineStart': 'medium none rgb(0, 0, 0)'
-'border-inline-start': 'medium none rgb(0, 0, 0)'
+'borderInlineStart': 'rgb(0, 0, 0)'
+'border-inline-start': 'rgb(0, 0, 0)'
 'borderInlineStartColor': 'rgb(0, 0, 0)'
 'border-inline-start-color': 'rgb(0, 0, 0)'
 'borderInlineStartStyle': 'none'
 'border-inline-start-style': 'none'
 'borderInlineStartWidth': 'medium'
 'border-inline-start-width': 'medium'
-'borderLeft': '0px none rgb(0, 0, 0)'
-'border-left': '0px none rgb(0, 0, 0)'
+'borderLeft': '0px rgb(0, 0, 0)'
+'border-left': '0px rgb(0, 0, 0)'
 'borderLeftColor': 'rgb(0, 0, 0)'
 'border-left-color': 'rgb(0, 0, 0)'
 'borderLeftStyle': 'none'
@@ -243,8 +243,8 @@ All supported properties and their default values exposed from CSSStylePropertie
 'border-left-width': '0px'
 'borderRadius': '0px'
 'border-radius': '0px'
-'borderRight': '0px none rgb(0, 0, 0)'
-'border-right': '0px none rgb(0, 0, 0)'
+'borderRight': '0px rgb(0, 0, 0)'
+'border-right': '0px rgb(0, 0, 0)'
 'borderRightColor': 'rgb(0, 0, 0)'
 'border-right-color': 'rgb(0, 0, 0)'
 'borderRightStyle': 'none'
@@ -255,8 +255,8 @@ All supported properties and their default values exposed from CSSStylePropertie
 'border-spacing': '0px'
 'borderStyle': 'none'
 'border-style': 'none'
-'borderTop': '0px none rgb(0, 0, 0)'
-'border-top': '0px none rgb(0, 0, 0)'
+'borderTop': '0px rgb(0, 0, 0)'
+'border-top': '0px rgb(0, 0, 0)'
 'borderTopColor': 'rgb(0, 0, 0)'
 'border-top-color': 'rgb(0, 0, 0)'
 'borderTopLeftRadius': '0px'
@@ -496,7 +496,7 @@ All supported properties and their default values exposed from CSSStylePropertie
 'object-position': '50% 50%'
 'opacity': '1'
 'order': '0'
-'outline': 'rgb(0, 0, 0) none 0px'
+'outline': 'rgb(0, 0, 0) 0px'
 'outlineColor': 'rgb(0, 0, 0)'
 'outline-color': 'rgb(0, 0, 0)'
 'outlineOffset': '0px'
@@ -606,7 +606,7 @@ All supported properties and their default values exposed from CSSStylePropertie
 'transform-box': 'view-box'
 'transformOrigin': '50% 50%'
 'transform-origin': '50% 50%'
-'transition': 'all 0s ease 0s'
+'transition': 'all'
 'transitionDelay': '0s'
 'transition-delay': '0s'
 'transitionDuration': '0s'
diff --git a/Tests/LibWeb/Text/expected/wpt-import/css/css-backgrounds/parsing/border-valid.txt b/Tests/LibWeb/Text/expected/wpt-import/css/css-backgrounds/parsing/border-valid.txt
new file mode 100644
index 00000000000..412ec03ba4e
--- /dev/null
+++ b/Tests/LibWeb/Text/expected/wpt-import/css/css-backgrounds/parsing/border-valid.txt
@@ -0,0 +1,11 @@
+Harness status: OK
+
+Found 6 tests
+
+6 Pass
+Pass	e.style['border'] = "1px dotted red" should set the property value
+Pass	e.style['border'] = "green double thin" should set the property value
+Pass	e.style['border-top'] = "thin" should set the property value
+Pass	e.style['border-right'] = "double" should set the property value
+Pass	e.style['border-bottom'] = "green" should set the property value
+Pass	e.style['border-left'] = "1px dotted red" should set the property value
\ No newline at end of file
diff --git a/Tests/LibWeb/Text/expected/wpt-import/css/css-ui/parsing/outline-valid.txt b/Tests/LibWeb/Text/expected/wpt-import/css/css-ui/parsing/outline-valid.txt
new file mode 100644
index 00000000000..26525257348
--- /dev/null
+++ b/Tests/LibWeb/Text/expected/wpt-import/css/css-ui/parsing/outline-valid.txt
@@ -0,0 +1,25 @@
+Harness status: OK
+
+Found 20 tests
+
+20 Pass
+Pass	e.style['outline'] = "rgba(10, 20, 30, 0.4)" should set the property value
+Pass	e.style['outline'] = "auto" should set the property value
+Pass	e.style['outline'] = "none" should set the property value
+Pass	e.style['outline'] = "dotted" should set the property value
+Pass	e.style['outline'] = "dashed" should set the property value
+Pass	e.style['outline'] = "solid" should set the property value
+Pass	e.style['outline'] = "double" should set the property value
+Pass	e.style['outline'] = "groove" should set the property value
+Pass	e.style['outline'] = "ridge" should set the property value
+Pass	e.style['outline'] = "inset" should set the property value
+Pass	e.style['outline'] = "outset" should set the property value
+Pass	e.style['outline'] = "0" should set the property value
+Pass	e.style['outline'] = "1px" should set the property value
+Pass	e.style['outline'] = "calc(2em + 3ex)" should set the property value
+Pass	e.style['outline'] = "thin" should set the property value
+Pass	e.style['outline'] = "medium" should set the property value
+Pass	e.style['outline'] = "thick" should set the property value
+Pass	e.style['outline'] = "dashed thin" should set the property value
+Pass	e.style['outline'] = "medium rgba(10, 20, 30, 0.4)" should set the property value
+Pass	e.style['outline'] = "3px ridge rgba(10, 20, 30, 0.4)" should set the property value
\ No newline at end of file
diff --git a/Tests/LibWeb/Text/input/wpt-import/css/css-backgrounds/parsing/border-valid.html b/Tests/LibWeb/Text/input/wpt-import/css/css-backgrounds/parsing/border-valid.html
new file mode 100644
index 00000000000..ff4a03e6e29
--- /dev/null
+++ b/Tests/LibWeb/Text/input/wpt-import/css/css-backgrounds/parsing/border-valid.html
@@ -0,0 +1,23 @@
+<!DOCTYPE html>
+<html>
+<head>
+<meta charset="utf-8">
+<title>CSS Backgrounds and Borders Module Level 3: parsing border with valid values</title>
+<link rel="help" href="https://drafts.csswg.org/css-backgrounds/#border-shorthands">
+<meta name="assert" content="border supports the full grammar '<line-width> || <line-style> || <color>'.">
+<script src="../../../resources/testharness.js"></script>
+<script src="../../../resources/testharnessreport.js"></script>
+<script src="../../../css/support/parsing-testcommon.js"></script>
+</head>
+<body>
+<script>
+test_valid_value("border", "1px dotted red");
+test_valid_value("border", "green double thin", "thin double green");
+
+test_valid_value("border-top", "thin", ["thin", "thin none"]);
+test_valid_value("border-right", "double", ["double", "medium double"]);
+test_valid_value("border-bottom", "green", ["green", "medium none green"]);
+test_valid_value("border-left", "1px dotted red");
+</script>
+</body>
+</html>
diff --git a/Tests/LibWeb/Text/input/wpt-import/css/css-ui/parsing/outline-valid.html b/Tests/LibWeb/Text/input/wpt-import/css/css-ui/parsing/outline-valid.html
new file mode 100644
index 00000000000..3a7ee5a2e0a
--- /dev/null
+++ b/Tests/LibWeb/Text/input/wpt-import/css/css-ui/parsing/outline-valid.html
@@ -0,0 +1,43 @@
+<!DOCTYPE html>
+<html>
+<head>
+<meta charset="utf-8">
+<title>CSS UI Level 3: parsing outline with valid values</title>
+<link rel="author" title="Eric Willigers" href="mailto:ericwilligers@chromium.org">
+<link rel="help" href="https://drafts.csswg.org/css-ui-3/#outline">
+<link rel="help" href="https://drafts.csswg.org/cssom/#serializing-css-values">
+<meta name="assert" content="outline supports the full grammar '<outline-color> || <outline> || <outline>'.">
+<meta name="assert" content="outline serializes in canonical order, with shortest possible serialization.">
+<script src="../../../resources/testharness.js"></script>
+<script src="../../../resources/testharnessreport.js"></script>
+<script src="../../../css/support/parsing-testcommon.js"></script>
+</head>
+<body>
+<script>
+test_valid_value("outline", "rgba(10, 20, 30, 0.4)");
+
+test_valid_value("outline", "auto");
+test_valid_value("outline", "none", ["currentcolor", "none", "medium"]);
+test_valid_value("outline", "dotted");
+test_valid_value("outline", "dashed");
+test_valid_value("outline", "solid");
+test_valid_value("outline", "double");
+test_valid_value("outline", "groove");
+test_valid_value("outline", "ridge");
+test_valid_value("outline", "inset");
+test_valid_value("outline", "outset");
+
+test_valid_value("outline", "0", "0px");
+test_valid_value("outline", "1px");
+test_valid_value("outline", "calc(2em + 3ex)");
+test_valid_value("outline", "thin");
+test_valid_value("outline", "medium", ["currentcolor", "none", "medium"]);
+test_valid_value("outline", "thick");
+
+test_valid_value("outline", "dashed thin");
+test_valid_value("outline", "medium rgba(10, 20, 30, 0.4)", ["rgba(10, 20, 30, 0.4) medium", "rgba(10, 20, 30, 0.4)"]);
+
+test_valid_value("outline", "3px ridge rgba(10, 20, 30, 0.4)", "rgba(10, 20, 30, 0.4) ridge 3px");
+</script>
+</body>
+</html>