diff --git a/testing/web-platform/tests/css/css-position/overlay/overlay-user-agent-rules.html b/testing/web-platform/tests/css/css-position/overlay/overlay-user-agent-rules.html
new file mode 100644
index 000000000000..b2a967cf6ed9
--- /dev/null
+++ b/testing/web-platform/tests/css/css-position/overlay/overlay-user-agent-rules.html
@@ -0,0 +1,419 @@
+<
+!
+DOCTYPE
+html
+>
+<
+link
+rel
+=
+author
+href
+=
+"
+mailto
+:
+jarhar
+chromium
+.
+org
+"
+>
+<
+link
+rel
+=
+help
+href
+=
+"
+https
+:
+/
+/
+github
+.
+com
+/
+whatwg
+/
+html
+/
+pull
+/
+9093
+"
+>
+<
+link
+rel
+=
+help
+href
+=
+"
+https
+:
+/
+/
+drafts
+.
+csswg
+.
+org
+/
+css
+-
+position
+-
+4
+/
+#
+overlay
+"
+>
+<
+script
+src
+=
+"
+/
+resources
+/
+testharness
+.
+js
+"
+>
+<
+/
+script
+>
+<
+script
+src
+=
+"
+/
+resources
+/
+testharnessreport
+.
+js
+"
+>
+<
+/
+script
+>
+<
+title
+>
+CSS
+Position
+Test
+:
+User
+agent
+style
+for
+overlay
+<
+/
+title
+>
+<
+style
+>
+div
+{
+overlay
+:
+auto
+;
+}
+<
+/
+style
+>
+<
+body
+>
+<
+script
+>
+test
+(
+(
+)
+=
+>
+{
+const
+div
+=
+document
+.
+createElement
+(
+'
+div
+'
+)
+;
+document
+.
+body
+.
+appendChild
+(
+div
+)
+;
+div
+.
+style
+.
+overlay
+=
+'
+auto
+'
+;
+assert_equals
+(
+getComputedStyle
+(
+div
+)
+.
+overlay
+'
+none
+'
+)
+;
+}
+'
+HTML
+elements
+should
+have
+overlay
+:
+none
+!
+important
+from
+the
+user
+-
+agent
+.
+'
+)
+;
+test
+(
+(
+)
+=
+>
+{
+const
+svg
+=
+document
+.
+createElement
+(
+'
+svg
+'
+)
+;
+document
+.
+body
+.
+appendChild
+(
+svg
+)
+;
+svg
+.
+style
+.
+overlay
+=
+'
+auto
+'
+;
+assert_equals
+(
+getComputedStyle
+(
+svg
+)
+.
+overlay
+'
+none
+'
+)
+;
+}
+'
+SVG
+elements
+should
+have
+overlay
+:
+none
+!
+important
+from
+the
+user
+-
+agent
+.
+'
+)
+;
+test
+(
+(
+)
+=
+>
+{
+const
+nullNamespace
+=
+document
+.
+createElementNS
+(
+null
+'
+div
+'
+)
+;
+document
+.
+body
+.
+appendChild
+(
+nullNamespace
+)
+;
+assert_equals
+(
+getComputedStyle
+(
+nullNamespace
+)
+.
+overlay
+'
+none
+'
+)
+;
+}
+'
+Null
+namespace
+elements
+should
+have
+overlay
+:
+none
+!
+important
+from
+the
+user
+-
+agent
+.
+'
+)
+;
+test
+(
+(
+)
+=
+>
+{
+const
+weirdNamespace
+=
+document
+.
+createElementNS
+(
+'
+hello
+world
+'
+'
+div
+'
+)
+;
+document
+.
+body
+.
+appendChild
+(
+weirdNamespace
+)
+;
+assert_equals
+(
+getComputedStyle
+(
+weirdNamespace
+)
+.
+overlay
+'
+none
+'
+)
+;
+}
+'
+Arbitrary
+namespace
+elements
+should
+have
+overlay
+:
+none
+!
+important
+from
+the
+user
+-
+agent
+.
+'
+)
+;
+<
+/
+script
+>