diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index d1fd7dc6e..8052c26ae 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -27,10 +27,10 @@ jobs:
           python: 3.9
           docutils: du16
           coverage: "--cov ./ --cov-append --cov-config setup.cfg"
-        - name: py310-dev
-          python: 3.10-dev
-          docutils: du17
-          os: ubuntu-latest  # required
+        # - name: py310-dev
+        #   python: 3.10-dev
+        #   docutils: du17
+        #   os: ubuntu-latest  # required
     env:
       PYTEST_ADDOPTS: ${{ matrix.coverage }}
 
diff --git a/CHANGES b/CHANGES
index baf868e05..b7cb2554a 100644
--- a/CHANGES
+++ b/CHANGES
@@ -1,11 +1,9 @@
-Release 3.5.4 (in development)
+Release 3.5.5 (in development)
 ==============================
 
 Dependencies
 ------------
 
-* #9071: Restrict docutils to 0.16
-
 Incompatible changes
 --------------------
 
@@ -18,14 +16,28 @@ Features added
 Bugs fixed
 ----------
 
-* #9078: autodoc: Async staticmethods and classmethods are considered as non
-  async coroutine-functions with Python3.10
-* #8870: The style of toctree captions has been changed with docutils-0.17
-* #9001: The style of ``sidebar`` directive has been changed with docutils-0.17
-
 Testing
 --------
 
+Release 3.5.4 (released Apr 11, 2021)
+=====================================
+
+Dependencies
+------------
+
+* #9071: Restrict docutils to 0.16
+
+Bugs fixed
+----------
+
+* #9078: autodoc: Async staticmethods and classmethods are considered as non
+  async coroutine-functions with Python3.10
+* #8870, #9001, #9051: html theme: The style are not applied with docutils-0.17
+
+  - toctree captions
+  - The content of ``sidebar`` directive
+  - figures
+
 Release 3.5.3 (released Mar 20, 2021)
 =====================================
 
diff --git a/sphinx/__init__.py b/sphinx/__init__.py
index e72c9f81c..5a4c931e7 100644
--- a/sphinx/__init__.py
+++ b/sphinx/__init__.py
@@ -32,8 +32,8 @@ if 'PYTHONWARNINGS' not in os.environ:
 warnings.filterwarnings('ignore', "'U' mode is deprecated",
                         DeprecationWarning, module='docutils.io')
 
-__version__ = '3.5.4+'
-__released__ = '3.5.4'  # used when Sphinx builds its own docs
+__version__ = '3.5.5+'
+__released__ = '3.5.5'  # used when Sphinx builds its own docs
 
 #: Version info for better programmatic use.
 #:
@@ -43,7 +43,7 @@ __released__ = '3.5.4'  # used when Sphinx builds its own docs
 #:
 #: .. versionadded:: 1.2
 #:    Before version 1.2, check the string ``sphinx.__version__``.
-version_info = (3, 5, 4, 'beta', 0)
+version_info = (3, 5, 5, 'final', 0)
 
 package_dir = path.abspath(path.dirname(__file__))
 
diff --git a/sphinx/themes/agogo/static/agogo.css_t b/sphinx/themes/agogo/static/agogo.css_t
index 489ec17ea..0c78e4345 100644
--- a/sphinx/themes/agogo/static/agogo.css_t
+++ b/sphinx/themes/agogo/static/agogo.css_t
@@ -370,19 +370,25 @@ div.footer .left {
 
 /* Styles copied from basic theme */
 
-img.align-left, .figure.align-left, object.align-left {
+img.align-left, figure.align-left, .figure.align-left, object.align-left {
     clear: left;
     float: left;
     margin-right: 1em;
 }
 
-img.align-right, .figure.align-right, object.align-right {
+img.align-right, figure.align-right, .figure.align-right, object.align-right {
     clear: right;
     float: right;
     margin-left: 1em;
 }
 
-img.align-center, .figure.align-center, object.align-center {
+img.align-center, figure.align-center, .figure.align-center, object.align-center {
+  display: block;
+  margin-left: auto;
+  margin-right: auto;
+}
+
+img.align-default, figure.align-default, .figure.align-default {
   display: block;
   margin-left: auto;
   margin-right: auto;
@@ -407,11 +413,13 @@ table caption span.caption-number {
 table caption span.caption-text {
 }
 
-div.figure p.caption span.caption-number {
+div.figure p.caption span.caption-number,
+figcaption span.caption-number {
     font-style: italic;
 }
 
-div.figure p.caption span.caption-text {
+div.figure p.caption span.caption-text,
+figcaption span.caption-text {
 }
 
 /* -- search page ----------------------------------------------------------- */
diff --git a/sphinx/themes/basic/static/basic.css_t b/sphinx/themes/basic/static/basic.css_t
index 5fc83c848..c0158b27b 100644
--- a/sphinx/themes/basic/static/basic.css_t
+++ b/sphinx/themes/basic/static/basic.css_t
@@ -277,25 +277,25 @@ p.rubric {
     font-weight: bold;
 }
 
-img.align-left, .figure.align-left, object.align-left {
+img.align-left, figure.align-left, .figure.align-left, object.align-left {
     clear: left;
     float: left;
     margin-right: 1em;
 }
 
-img.align-right, .figure.align-right, object.align-right {
+img.align-right, figure.align-right, .figure.align-right, object.align-right {
     clear: right;
     float: right;
     margin-left: 1em;
 }
 
-img.align-center, .figure.align-center, object.align-center {
+img.align-center, figure.align-center, .figure.align-center, object.align-center {
   display: block;
   margin-left: auto;
   margin-right: auto;
 }
 
-img.align-default, .figure.align-default {
+img.align-default, figure.align-default, .figure.align-default {
   display: block;
   margin-left: auto;
   margin-right: auto;
@@ -458,20 +458,22 @@ td > :last-child {
 
 /* -- figures --------------------------------------------------------------- */
 
-div.figure {
+div.figure, figure {
     margin: 0.5em;
     padding: 0.5em;
 }
 
-div.figure p.caption {
+div.figure p.caption, figcaption {
     padding: 0.3em;
 }
 
-div.figure p.caption span.caption-number {
+div.figure p.caption span.caption-number,
+figcaption span.caption-number {
     font-style: italic;
 }
 
-div.figure p.caption span.caption-text {
+div.figure p.caption span.caption-text,
+figcaption span.caption-text {
 }
 
 /* -- field list styles ----------------------------------------------------- */
diff --git a/sphinx/themes/epub/static/epub.css_t b/sphinx/themes/epub/static/epub.css_t
index 46bbb93b3..9c9ca8565 100644
--- a/sphinx/themes/epub/static/epub.css_t
+++ b/sphinx/themes/epub/static/epub.css_t
@@ -325,11 +325,13 @@ table.citation td {
 
 /* -- figures --------------------------------------------------------------- */
 
-div.figure p.caption span.caption-number {
+div.figure p.caption span.caption-number,
+figcaption span.caption-number {
     font-style: italic;
 }
 
-div.figure p.caption span.caption-text {
+div.figure p.caption span.caption-text,
+figcaption span.caption-text {
 }
 
 /* -- field list styles ----------------------------------------------------- */
diff --git a/sphinx/themes/nonav/static/nonav.css b/sphinx/themes/nonav/static/nonav.css
index 63abb9f0d..c2d28a26b 100644
--- a/sphinx/themes/nonav/static/nonav.css
+++ b/sphinx/themes/nonav/static/nonav.css
@@ -314,11 +314,13 @@ table.citation td {
 
 /* -- figures --------------------------------------------------------------- */
 
-div.figure p.caption span.caption-number {
+div.figure p.caption span.caption-number,
+figcaption span.caption-number {
     font-style: italic;
 }
 
-div.figure p.caption span.caption-text {
+div.figure p.caption span.caption-text,
+figcaption span.caption-text {
 }
 
 /* -- field list styles ----------------------------------------------------- */
diff --git a/sphinx/themes/scrolls/static/scrolls.css_t b/sphinx/themes/scrolls/static/scrolls.css_t
index f039d9e2b..48b5af5fe 100644
--- a/sphinx/themes/scrolls/static/scrolls.css_t
+++ b/sphinx/themes/scrolls/static/scrolls.css_t
@@ -478,11 +478,13 @@ div.viewcode-block:target {
     padding: 0 5px;
 }
 
-div.figure p.caption span.caption-number {
+div.figure p.caption span.caption-number,
+figcaption span.caption-number {
     font-style: italic;
 }
 
-div.figure p.caption span.caption-text {
+div.figure p.caption span.caption-text,
+figcaption span.caption-text {
 }
 
 /* math display */
diff --git a/sphinx/themes/traditional/static/traditional.css_t b/sphinx/themes/traditional/static/traditional.css_t
index 4371d8e89..bd648b47e 100644
--- a/sphinx/themes/traditional/static/traditional.css_t
+++ b/sphinx/themes/traditional/static/traditional.css_t
@@ -743,11 +743,13 @@ div.literal-block-wrapper pre {
     margin: 0;
 }
 
-div.figure p.caption span.caption-number {
+div.figure p.caption span.caption-number,
+figcaption span.caption-number {
     font-style: italic;
 }
 
-div.figure p.caption span.caption-text {
+div.figure p.caption span.caption-text,
+figcaption span.caption-text {
 }
 
 /* :::: MATH DISPLAY :::: */