diff --git a/testing/web-platform/tests/css/css-flexbox/flex-item-contains-strict.html b/testing/web-platform/tests/css/css-flexbox/flex-item-contains-strict.html
new file mode 100644
index 0000000000000..5532373bdc76b
--- /dev/null
+++ b/testing/web-platform/tests/css/css-flexbox/flex-item-contains-strict.html
@@ -0,0 +1,976 @@
+<
+!
+DOCTYPE
+html
+>
+<
+title
+>
+CSS
+Flexbox
+:
+'
+contain
+'
+property
+strict
+value
+<
+/
+title
+>
+<
+link
+rel
+=
+"
+help
+"
+href
+=
+"
+https
+:
+/
+/
+drafts
+.
+csswg
+.
+org
+/
+css
+-
+contain
+/
+#
+contain
+-
+property
+"
+>
+<
+link
+rel
+=
+"
+help
+"
+href
+=
+"
+https
+:
+/
+/
+drafts
+.
+csswg
+.
+org
+/
+css
+-
+flexbox
+/
+#
+flex
+-
+containers
+"
+>
+<
+link
+rel
+=
+"
+help
+"
+href
+=
+"
+https
+:
+/
+/
+drafts
+.
+csswg
+.
+org
+/
+css
+-
+flexbox
+/
+#
+flex
+-
+direction
+-
+property
+"
+>
+<
+link
+rel
+=
+"
+help
+"
+href
+=
+"
+https
+:
+/
+/
+drafts
+.
+csswg
+.
+org
+/
+css
+-
+flexbox
+/
+#
+align
+-
+items
+-
+property
+"
+>
+<
+meta
+name
+=
+"
+assert
+"
+content
+=
+"
+This
+test
+ensures
+that
+the
+strict
+value
+of
+the
+'
+contain
+'
+property
+in
+combination
+with
+mixing
+of
+'
+display
+'
+inline
+-
+flex
+value
+'
+align
+-
+items
+'
+flex
+-
+start
+value
+column
+direction
+works
+properly
+.
+"
+>
+<
+style
+>
+.
+inline
+-
+flex
+{
+display
+:
+inline
+-
+flex
+;
+outline
+:
+solid
+;
+background
+:
+red
+;
+}
+<
+/
+style
+>
+<
+script
+src
+=
+"
+/
+resources
+/
+testharness
+.
+js
+"
+>
+<
+/
+script
+>
+<
+script
+src
+=
+"
+/
+resources
+/
+testharnessreport
+.
+js
+"
+>
+<
+/
+script
+>
+<
+script
+src
+=
+"
+/
+resources
+/
+check
+-
+layout
+-
+th
+.
+js
+"
+>
+<
+/
+script
+>
+<
+body
+onload
+=
+"
+checkLayout
+(
+'
+.
+inline
+-
+flex
+'
+)
+"
+>
+<
+p
+>
+Stretched
+:
+<
+/
+p
+>
+<
+div
+class
+=
+"
+inline
+-
+flex
+"
+style
+=
+"
+display
+:
+inline
+-
+flex
+;
+flex
+-
+direction
+:
+column
+;
+"
+data
+-
+expected
+-
+width
+=
+"
+0
+"
+data
+-
+expected
+-
+height
+=
+"
+0
+"
+>
+<
+div
+style
+=
+"
+contain
+:
+strict
+;
+"
+data
+-
+expected
+-
+width
+=
+"
+0
+"
+data
+-
+expected
+-
+height
+=
+"
+0
+"
+>
+Column
+<
+/
+div
+>
+<
+/
+div
+>
+<
+div
+class
+=
+"
+inline
+-
+flex
+"
+data
+-
+expected
+-
+width
+=
+"
+0
+"
+data
+-
+expected
+-
+height
+=
+"
+0
+"
+>
+<
+div
+style
+=
+"
+contain
+:
+strict
+;
+"
+data
+-
+expected
+-
+width
+=
+"
+0
+"
+data
+-
+expected
+-
+height
+=
+"
+0
+"
+>
+Row
+<
+/
+div
+>
+<
+/
+div
+>
+<
+div
+class
+=
+"
+inline
+-
+flex
+"
+style
+=
+"
+display
+:
+inline
+-
+flex
+;
+flex
+-
+direction
+:
+column
+;
+"
+data
+-
+expected
+-
+width
+=
+"
+30
+"
+data
+-
+expected
+-
+height
+=
+"
+30
+"
+>
+<
+div
+style
+=
+"
+contain
+:
+strict
+;
+width
+:
+30px
+;
+height
+:
+30px
+;
+"
+data
+-
+expected
+-
+width
+=
+"
+30
+"
+data
+-
+expected
+-
+height
+=
+"
+30
+"
+>
+Column
+<
+/
+div
+>
+<
+/
+div
+>
+<
+div
+class
+=
+"
+inline
+-
+flex
+"
+style
+=
+"
+display
+:
+inline
+-
+flex
+;
+"
+data
+-
+expected
+-
+width
+=
+"
+30
+"
+data
+-
+expected
+-
+height
+=
+"
+30
+"
+>
+<
+div
+style
+=
+"
+contain
+:
+strict
+;
+width
+:
+30px
+;
+height
+:
+30px
+;
+"
+data
+-
+expected
+-
+width
+=
+"
+30
+"
+data
+-
+expected
+-
+height
+=
+"
+30
+"
+>
+Row
+<
+/
+div
+>
+<
+/
+div
+>
+<
+p
+>
+Flex
+-
+start
+:
+<
+/
+p
+>
+<
+div
+class
+=
+"
+inline
+-
+flex
+"
+style
+=
+"
+flex
+-
+direction
+:
+column
+;
+align
+-
+items
+:
+flex
+-
+start
+;
+"
+data
+-
+expected
+-
+width
+=
+"
+0
+"
+data
+-
+expected
+-
+height
+=
+"
+0
+"
+>
+<
+div
+style
+=
+"
+contain
+:
+strict
+;
+"
+data
+-
+expected
+-
+width
+=
+"
+0
+"
+data
+-
+expected
+-
+height
+=
+"
+0
+"
+>
+Column
+<
+/
+div
+>
+<
+/
+div
+>
+<
+div
+class
+=
+"
+inline
+-
+flex
+"
+style
+=
+"
+align
+-
+items
+:
+flex
+-
+start
+;
+"
+data
+-
+expected
+-
+width
+=
+"
+0
+"
+data
+-
+expected
+-
+height
+=
+"
+0
+"
+>
+<
+div
+style
+=
+"
+contain
+:
+strict
+;
+"
+data
+-
+expected
+-
+width
+=
+"
+0
+"
+data
+-
+expected
+-
+height
+=
+"
+0
+"
+>
+Row
+<
+/
+div
+>
+<
+/
+div
+>
+<
+div
+class
+=
+"
+inline
+-
+flex
+"
+style
+=
+"
+flex
+-
+direction
+:
+column
+;
+align
+-
+items
+:
+flex
+-
+start
+;
+"
+data
+-
+expected
+-
+width
+=
+"
+30
+"
+data
+-
+expected
+-
+height
+=
+"
+30
+"
+>
+<
+div
+style
+=
+"
+contain
+:
+strict
+;
+width
+:
+30px
+;
+height
+:
+30px
+;
+"
+data
+-
+expected
+-
+width
+=
+"
+30
+"
+data
+-
+expected
+-
+height
+=
+"
+30
+"
+>
+Column
+<
+/
+div
+>
+<
+/
+div
+>
+<
+div
+class
+=
+"
+inline
+-
+flex
+"
+style
+=
+"
+align
+-
+items
+:
+flex
+-
+start
+;
+"
+data
+-
+expected
+-
+width
+=
+"
+30
+"
+data
+-
+expected
+-
+height
+=
+"
+30
+"
+>
+<
+div
+style
+=
+"
+contain
+:
+strict
+;
+width
+:
+30px
+;
+height
+:
+30px
+;
+"
+data
+-
+expected
+-
+width
+=
+"
+30
+"
+data
+-
+expected
+-
+height
+=
+"
+30
+"
+>
+Row
+<
+/
+div
+>
+<
+/
+div
+>