diff --git a/css/css-position/sticky/position-sticky-fixed-ancestor-002.html b/css/css-position/sticky/position-sticky-fixed-ancestor-002.html
new file mode 100644
index 00000000000000..dc3c383ea5e9c8
--- /dev/null
+++ b/css/css-position/sticky/position-sticky-fixed-ancestor-002.html
@@ -0,0 +1,53 @@
+<!DOCTYPE html>
+
+  <meta charset="UTF-8">
+
+  <title>CSS Positioned Layout Test: a sticky element inside a fixed ancestor</title>
+
+  <link rel="author" title="Gérard Talbot" href="http://www.gtalbot.org/BrowserBugsSection/css21testsuite/">
+  <link rel="match" href="reference/position-sticky-fixed-ancestor-002-ref.html">
+  <link rel="help" href="https://www.w3.org/TR/css-position-3/#sticky-pos">
+
+  <meta name="flags" content="">
+
+  <style>
+  html, body, div
+    {
+      height: 100%;
+      margin: 0;
+      width: 100%;
+    }
+
+  div#positioned-container
+    {
+      background-color: red;
+      color: yellow;
+      font-size: 40vh;
+      position: absolute;
+    }
+
+  div#sticky
+    {
+      background-color: green;
+      bottom: 0;
+      color: white;
+      position: sticky;
+    }
+  </style>
+
+  <script type="text/javascript">
+  function startTest()
+  {
+  document.getElementById("positioned-container").style.position = "fixed";
+  }
+  </script>
+
+ <body onload="startTest();">
+
+    <div id="positioned-container">
+
+      <div id="vertical-spacer">FAIL</div>
+
+      <div id="sticky">PASS</div>
+
+    </div>
diff --git a/css/css-position/sticky/position-sticky-fixed-ancestor-003.html b/css/css-position/sticky/position-sticky-fixed-ancestor-003.html
new file mode 100644
index 00000000000000..382112cae42f13
--- /dev/null
+++ b/css/css-position/sticky/position-sticky-fixed-ancestor-003.html
@@ -0,0 +1,44 @@
+<!DOCTYPE html>
+
+  <meta charset="UTF-8">
+
+  <title>CSS Positioned Layout Test: a sticky element inside a fixed ancestor</title>
+
+  <link rel="author" title="Gérard Talbot" href="http://www.gtalbot.org/BrowserBugsSection/css21testsuite/">
+  <link rel="match" href="reference/position-sticky-fixed-ancestor-002-ref.html">
+  <link rel="help" href="https://www.w3.org/TR/css-position-3/#sticky-pos">
+
+  <meta name="flags" content="">
+
+  <style>
+  html, body, div
+    {
+      height: 100%;
+      margin: 0;
+      width: 100%;
+    }
+
+  div#fixed-container
+    {
+      background-color: red;
+      color: yellow;
+      font-size: 40vh;
+      position: fixed;
+    }
+
+  div#sticky
+    {
+      background-color: green;
+      bottom: 0;
+      color: white;
+      position: sticky;
+    }
+  </style>
+
+    <div id="fixed-container">
+
+      <div id="vertical-spacer">FAIL</div>
+
+      <div id="sticky">PASS</div>
+
+    </div>
diff --git a/css/css-position/sticky/position-sticky-scrolled-remove-sibling.html b/css/css-position/sticky/position-sticky-scrolled-remove-sibling.html
index f2cf8a98b30a2c..845454e1b3d6c5 100644
--- a/css/css-position/sticky/position-sticky-scrolled-remove-sibling.html
+++ b/css/css-position/sticky/position-sticky-scrolled-remove-sibling.html
@@ -1,21 +1,99 @@
 <!DOCTYPE html>
-<link rel="author" title="Morten Stenshorne" href="mailto:mstensho@chromium.org">
-<link rel="help" href="https://www.w3.org/TR/css-position-3/#sticky-pos">
-<p>Test passes if there is a filled green square, and no scrollbars</p>
-<div id="container" style="overflow:auto; width:100px; height:100px; background:red;">
-  <div style="position:sticky; top:0; height:100px; background:green;"></div>
-  <div id="bigItem" style="height:600px;"></div>
-</div>
-<script src="/resources/testharness.js"></script>
-<script src="/resources/testharnessreport.js"></script>
-<script>
-  container.scrollTop = 600;
-  requestAnimationFrame(()=>{
-    requestAnimationFrame(()=>{
-      bigItem.style.display = "none";
-      test(()=> {
-        assert_equals(container.scrollHeight, 100);
-      }, "Sticky position and its overflow contribution");
-    });
-  });
-</script>
+
+  <meta charset="UTF-8">
+
+  <title>CSS Positioned Layout Test: element with 'position: sticky' and removing a sibling in the vertical axis and in the horizontal axis</title>
+
+  <link rel="author" title="Morten Stenshorne" href="mailto:mstensho@chromium.org">
+  <link rel="author" title="Gérard Talbot" href="http://www.gtalbot.org/BrowserBugsSection/css21testsuite/">
+  <link rel="help" href="https://www.w3.org/TR/css-position-3/#sticky-pos">
+
+  <meta name="flags" content="">
+
+  <style>
+  div#scrollingContainerVert
+    {
+      background-color: red;
+      height: 100px;
+      overflow: auto;
+      width: 200px;
+    }
+
+  div#scrollingContainerHoriz
+    {
+      background-color: red;
+      height: 100px;
+      overflow-x: auto;
+      overflow-y: hidden;
+      width: 200px;
+    }
+
+  div#elemStickyVert
+    {
+      background-color: green;
+      height: 100px;
+      position: sticky;
+      top: 0px;
+    }
+
+  div#scrollingContainerHoriz > div
+    {
+      display: inline-block;
+      height: 100%;
+    }
+
+  div#elemStickyHoriz
+    {
+      background-color: green;
+      left: 0px;
+      position: sticky;
+      width: 200px;
+    }
+
+  div#tallItem
+    {
+      height: 600px;
+    }
+
+  div#wideItem
+    {
+      width: 600px;
+    }
+  </style>
+
+
+  <script src="/resources/testharness.js"></script>
+
+  <script src="/resources/testharnessreport.js"></script>
+
+  <p>Test passes if there is a filled green square and <strong>no scrollbar</strong>.
+
+  <div id="scrollingContainerVert">
+
+    <div id="elemStickyVert"></div>
+
+    <div id="tallItem"></div>
+
+  </div>
+
+
+  <div id="scrollingContainerHoriz">
+
+    <div id="elemStickyHoriz"></div><div id="wideItem"></div>
+
+  </div>
+
+
+  <script>
+  test(()=> {
+  scrollingContainerVert.scrollTop = 600;
+  tallItem.style.display = "none";
+  assert_equals(scrollingContainerVert.scrollHeight, 100);
+  }, "Sticky position and its overflow contribution in the vertical axis");
+
+  test(()=> {
+  scrollingContainerHoriz.scrollLeft = 600;
+  wideItem.style.display = "none";
+  assert_equals(scrollingContainerHoriz.scrollWidth, 200);
+  }, "Sticky position and its overflow contribution in the horizontal axis");
+  </script>
diff --git a/css/css-position/sticky/position-sticky-stacking-context-002.html b/css/css-position/sticky/position-sticky-stacking-context-002.html
new file mode 100644
index 00000000000000..1cc162880a3755
--- /dev/null
+++ b/css/css-position/sticky/position-sticky-stacking-context-002.html
@@ -0,0 +1,47 @@
+<!DOCTYPE html>
+
+  <meta charset="UTF-8">
+
+  <title>CSS Positioned Layout Test: an element with 'position: sticky' creates a stacking context</title>
+
+  <link rel="author" title="Gérard Talbot" href="http://www.gtalbot.org/BrowserBugsSection/css21testsuite/">
+  <link rel="match" href="../../reference/ref-filled-green-100px-square.xht">
+  <link rel="help" href="https://www.w3.org/TR/css-position-3/#sticky-pos">
+
+  <meta name="assert" content="This test checks that an element with 'position: sticky' creates a stacking context. In this test, the first 2 divs have the same 'auto' z-index value but since div#sticky is last in document tree order, then it must overlap div#overlapped-red. The final div#overlap-bottom-half-of-sticky exists to make sure that the div#sticky is squeezed, is 'sandwiched' between the other 2.">
+
+  <style>
+  div
+    {
+      height: 100px;
+      width: 100px;
+    }
+
+  div#overlapped-red
+    {
+      background-color: red;
+      position: absolute;
+    }
+
+  div#sticky
+    {
+      background: linear-gradient(to bottom, green 51%, red 49%);
+      position: sticky;
+    }
+
+  div#overlap-bottom-half-of-sticky
+    {
+      background-color: green;
+      bottom: 50px;
+      height: 50px;
+      position: relative;
+    }
+  </style>
+
+  <p>Test passes if there is a filled green square and <strong>no red</strong>.
+
+  <div id="overlapped-red"></div>
+
+  <div id="sticky"></div>
+
+  <div id="overlap-bottom-half-of-sticky"></div>
diff --git a/css/css-position/sticky/reference/position-sticky-fixed-ancestor-002-ref.html b/css/css-position/sticky/reference/position-sticky-fixed-ancestor-002-ref.html
new file mode 100644
index 00000000000000..abdc1dbcfa7ea2
--- /dev/null
+++ b/css/css-position/sticky/reference/position-sticky-fixed-ancestor-002-ref.html
@@ -0,0 +1,20 @@
+<!DOCTYPE html>
+
+ <meta charset="UTF-8">
+
+ <title>CSS Reference File</title>
+
+  <link rel="author" title="Gérard Talbot" href="http://www.gtalbot.org/BrowserBugsSection/css21testsuite/">
+
+  <style>
+  html, body, div
+    {
+      background-color: green;
+      color: white;
+      font-size: 40vh;
+      height: 100%;
+      margin: 0;
+    }
+  </style>
+
+  <div>PASS</div>
