diff --git a/Doc/library/calendar.rst b/Doc/library/calendar.rst
index 41e9e28e0c0..a415b4792a6 100644
--- a/Doc/library/calendar.rst
+++ b/Doc/library/calendar.rst
@@ -147,7 +147,7 @@ it's the base calendar for all computations.
    This class can be used to generate HTML calendars.
 
 
-   :class:`HTMLCalendar` instances have the following methods:
+   :class:`!HTMLCalendar` instances have the following methods:
 
    .. method:: formatmonth(theyear, themonth, withyear=True)
 
@@ -171,6 +171,85 @@ it's the base calendar for all computations.
       output (defaulting to the system default encoding).
 
 
+   :class:`!HTMLCalendar` has the following attributes you can override to
+   customize the CSS classes used by the calendar:
+
+   .. attribute:: cssclasses
+
+      A list of CSS classes used for each weekday. The default class list is::
+
+         cssclasses = ["mon", "tue", "wed", "thu", "fri", "sat", "sun"]
+
+      more styles can be added for each day::
+
+         cssclasses = ["mon text-bold", "tue", "wed", "thu", "fri", "sat", "sun red"]
+
+      Note that the length of this list must be seven items.
+
+
+   .. attribute:: cssclass_noday
+
+      The CSS class for a weekday occurring in the previous or coming month.
+
+      .. versionadded:: 3.7
+
+
+   .. attribute:: cssclasses_weekday_head
+
+      A list of CSS classes used for weekday names in the header row.
+      The default is the same as :attr:`cssclasses`.
+
+      .. versionadded:: 3.7
+
+
+   .. attribute:: cssclass_month_head
+
+      The month's head CSS class (used by :meth:`formatmonthname`).
+      The default value is ``"month"``.
+
+      .. versionadded:: 3.7
+
+
+   .. attribute:: cssclass_month
+
+      The CSS class for the whole month's table (used by :meth:`formatmonth`).
+      The default value is ``"month"``.
+
+      .. versionadded:: 3.7
+
+
+   .. attribute:: cssclass_year
+
+      The CSS class for the whole year's table of tables (used by
+      :meth:`formatyear`). The default value is ``"year"``.
+
+      .. versionadded:: 3.7
+
+
+   .. attribute:: cssclass_year_head
+
+      The CSS class for the table head for the whole year (used by
+      :meth:`formatyear`). The default value is ``"year"``.
+
+      .. versionadded:: 3.7
+
+
+   Note that although the naming for the above described class attributes is
+   singular (e.g. ``cssclass_month`` ``cssclass_noday``), one can replace the
+   single CSS class with a space separated list of CSS classes, for example::
+
+         "text-bold text-red"
+
+   Here is an example how :class:`!HTMLCalendar` can be customized::
+
+       class CustomHTMLCal(calendar.HTMLCalendar):
+           cssclasses = [style + " text-nowrap" for style in
+                         calendar.HTMLCalendar.cssclasses]
+           cssclass_month_head = "text-center month-head"
+           cssclass_month = "text-center month"
+           cssclass_year = "text-italic lead"
+
+
 .. class:: LocaleTextCalendar(firstweekday=0, locale=None)
 
    This subclass of :class:`TextCalendar` can be passed a locale name in the
diff --git a/Doc/whatsnew/3.7.rst b/Doc/whatsnew/3.7.rst
index 761c85fd220..602db8c0ac8 100644
--- a/Doc/whatsnew/3.7.rst
+++ b/Doc/whatsnew/3.7.rst
@@ -103,13 +103,6 @@ New Modules
 Improved Modules
 ================
 
-cgi
----
-
-:func:`~cgi.parse_multipart` returns the same results as
-:class:`~FieldStorage` : for non-file fields, the value associated to a key
-is a list of strings, not bytes.
-(Contributed by Pierre Quentel in :issue:`29979`.)
 
 binascii
 --------
@@ -118,6 +111,22 @@ The :func:`~binascii.b2a_uu` function now accepts an optional *backtick*
 keyword argument.  When it's true, zeros are represented by ``'`'``
 instead of spaces.  (Contributed by Xiang Zhang in :issue:`30103`.)
 
+
+calendar
+--------
+
+The :class:`~calendar.HTMLCalendar` has added new class attribute which ease the
+customisation the CSS classes in the produced HTML calendar.
+(Contributed by Oz Tiram in :issue:`30095`.)
+
+cgi
+---
+
+:func:`~cgi.parse_multipart` returns the same results as
+:class:`~FieldStorage` : for non-file fields, the value associated to a key
+is a list of strings, not bytes.
+(Contributed by Pierre Quentel in :issue:`29979`.)
+
 contextlib
 ----------
 
diff --git a/Lib/calendar.py b/Lib/calendar.py
index 28ac56fdbe8..0218e2d3977 100644
--- a/Lib/calendar.py
+++ b/Lib/calendar.py
@@ -382,12 +382,31 @@ class HTMLCalendar(Calendar):
     # CSS classes for the day <td>s
     cssclasses = ["mon", "tue", "wed", "thu", "fri", "sat", "sun"]
 
+    # CSS classes for the day <th>s
+    cssclasses_weekday_head = cssclasses
+
+    # CSS class for the days before and after current month
+    cssclass_noday = "noday"
+
+    # CSS class for the month's head
+    cssclass_month_head = "month"
+
+    # CSS class for the month
+    cssclass_month = "month"
+
+    # CSS class for the year's table head
+    cssclass_year_head = "year"
+
+    # CSS class for the whole year table
+    cssclass_year = "year"
+
     def formatday(self, day, weekday):
         """
         Return a day as a table cell.
         """
         if day == 0:
-            return '<td class="noday">&nbsp;</td>' # day outside month
+            # day outside month
+            return '<td class="%s">&nbsp;</td>' % self.cssclass_noday
         else:
             return '<td class="%s">%d</td>' % (self.cssclasses[weekday], day)
 
@@ -402,7 +421,8 @@ def formatweekday(self, day):
         """
         Return a weekday name as a table header.
         """
-        return '<th class="%s">%s</th>' % (self.cssclasses[day], day_abbr[day])
+        return '<th class="%s">%s</th>' % (
+            self.cssclasses_weekday_head[day], day_abbr[day])
 
     def formatweekheader(self):
         """
@@ -419,7 +439,8 @@ def formatmonthname(self, theyear, themonth, withyear=True):
             s = '%s %s' % (month_name[themonth], theyear)
         else:
             s = '%s' % month_name[themonth]
-        return '<tr><th colspan="7" class="month">%s</th></tr>' % s
+        return '<tr><th colspan="7" class="%s">%s</th></tr>' % (
+            self.cssclass_month_head, s)
 
     def formatmonth(self, theyear, themonth, withyear=True):
         """
@@ -427,7 +448,8 @@ def formatmonth(self, theyear, themonth, withyear=True):
         """
         v = []
         a = v.append
-        a('<table border="0" cellpadding="0" cellspacing="0" class="month">')
+        a('<table border="0" cellpadding="0" cellspacing="0" class="%s">' % (
+            self.cssclass_month))
         a('\n')
         a(self.formatmonthname(theyear, themonth, withyear=withyear))
         a('\n')
@@ -447,9 +469,11 @@ def formatyear(self, theyear, width=3):
         v = []
         a = v.append
         width = max(width, 1)
-        a('<table border="0" cellpadding="0" cellspacing="0" class="year">')
+        a('<table border="0" cellpadding="0" cellspacing="0" class="%s">' %
+          self.cssclass_year)
         a('\n')
-        a('<tr><th colspan="%d" class="year">%s</th></tr>' % (width, theyear))
+        a('<tr><th colspan="%d" class="%s">%s</th></tr>' % (
+            width, self.cssclass_year_head, theyear))
         for i in range(January, January+12, width):
             # months in this row
             months = range(i, min(i+width, 13))
diff --git a/Lib/test/test_calendar.py b/Lib/test/test_calendar.py
index bd57653ffad..c777f648356 100644
--- a/Lib/test/test_calendar.py
+++ b/Lib/test/test_calendar.py
@@ -57,19 +57,22 @@
 25 26 27 28 29 30 31      29 30                     27 28 29 30 31
 """
 
+
+default_format = dict(year="year", month="month", encoding="ascii")
+
 result_2004_html = """\
-<?xml version="1.0" encoding="%(e)s"?>
+<?xml version="1.0" encoding="{encoding}"?>
 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
 <html>
 <head>
-<meta http-equiv="Content-Type" content="text/html; charset=%(e)s" />
+<meta http-equiv="Content-Type" content="text/html; charset={encoding}" />
 <link rel="stylesheet" type="text/css" href="calendar.css" />
 <title>Calendar for 2004</title>
 </head>
 <body>
-<table border="0" cellpadding="0" cellspacing="0" class="year">
-<tr><th colspan="3" class="year">2004</th></tr><tr><td><table border="0" cellpadding="0" cellspacing="0" class="month">
-<tr><th colspan="7" class="month">January</th></tr>
+<table border="0" cellpadding="0" cellspacing="0" class="{year}">
+<tr><th colspan="3" class="{year}">2004</th></tr><tr><td><table border="0" cellpadding="0" cellspacing="0" class="{month}">
+<tr><th colspan="7" class="{month}">January</th></tr>
 <tr><th class="mon">Mon</th><th class="tue">Tue</th><th class="wed">Wed</th><th class="thu">Thu</th><th class="fri">Fri</th><th class="sat">Sat</th><th class="sun">Sun</th></tr>
 <tr><td class="noday">&nbsp;</td><td class="noday">&nbsp;</td><td class="noday">&nbsp;</td><td class="thu">1</td><td class="fri">2</td><td class="sat">3</td><td class="sun">4</td></tr>
 <tr><td class="mon">5</td><td class="tue">6</td><td class="wed">7</td><td class="thu">8</td><td class="fri">9</td><td class="sat">10</td><td class="sun">11</td></tr>
@@ -77,8 +80,8 @@
 <tr><td class="mon">19</td><td class="tue">20</td><td class="wed">21</td><td class="thu">22</td><td class="fri">23</td><td class="sat">24</td><td class="sun">25</td></tr>
 <tr><td class="mon">26</td><td class="tue">27</td><td class="wed">28</td><td class="thu">29</td><td class="fri">30</td><td class="sat">31</td><td class="noday">&nbsp;</td></tr>
 </table>
-</td><td><table border="0" cellpadding="0" cellspacing="0" class="month">
-<tr><th colspan="7" class="month">February</th></tr>
+</td><td><table border="0" cellpadding="0" cellspacing="0" class="{month}">
+<tr><th colspan="7" class="{month}">February</th></tr>
 <tr><th class="mon">Mon</th><th class="tue">Tue</th><th class="wed">Wed</th><th class="thu">Thu</th><th class="fri">Fri</th><th class="sat">Sat</th><th class="sun">Sun</th></tr>
 <tr><td class="noday">&nbsp;</td><td class="noday">&nbsp;</td><td class="noday">&nbsp;</td><td class="noday">&nbsp;</td><td class="noday">&nbsp;</td><td class="noday">&nbsp;</td><td class="sun">1</td></tr>
 <tr><td class="mon">2</td><td class="tue">3</td><td class="wed">4</td><td class="thu">5</td><td class="fri">6</td><td class="sat">7</td><td class="sun">8</td></tr>
@@ -86,8 +89,8 @@
 <tr><td class="mon">16</td><td class="tue">17</td><td class="wed">18</td><td class="thu">19</td><td class="fri">20</td><td class="sat">21</td><td class="sun">22</td></tr>
 <tr><td class="mon">23</td><td class="tue">24</td><td class="wed">25</td><td class="thu">26</td><td class="fri">27</td><td class="sat">28</td><td class="sun">29</td></tr>
 </table>
-</td><td><table border="0" cellpadding="0" cellspacing="0" class="month">
-<tr><th colspan="7" class="month">March</th></tr>
+</td><td><table border="0" cellpadding="0" cellspacing="0" class="{month}">
+<tr><th colspan="7" class="{month}">March</th></tr>
 <tr><th class="mon">Mon</th><th class="tue">Tue</th><th class="wed">Wed</th><th class="thu">Thu</th><th class="fri">Fri</th><th class="sat">Sat</th><th class="sun">Sun</th></tr>
 <tr><td class="mon">1</td><td class="tue">2</td><td class="wed">3</td><td class="thu">4</td><td class="fri">5</td><td class="sat">6</td><td class="sun">7</td></tr>
 <tr><td class="mon">8</td><td class="tue">9</td><td class="wed">10</td><td class="thu">11</td><td class="fri">12</td><td class="sat">13</td><td class="sun">14</td></tr>
@@ -95,8 +98,8 @@
 <tr><td class="mon">22</td><td class="tue">23</td><td class="wed">24</td><td class="thu">25</td><td class="fri">26</td><td class="sat">27</td><td class="sun">28</td></tr>
 <tr><td class="mon">29</td><td class="tue">30</td><td class="wed">31</td><td class="noday">&nbsp;</td><td class="noday">&nbsp;</td><td class="noday">&nbsp;</td><td class="noday">&nbsp;</td></tr>
 </table>
-</td></tr><tr><td><table border="0" cellpadding="0" cellspacing="0" class="month">
-<tr><th colspan="7" class="month">April</th></tr>
+</td></tr><tr><td><table border="0" cellpadding="0" cellspacing="0" class="{month}">
+<tr><th colspan="7" class="{month}">April</th></tr>
 <tr><th class="mon">Mon</th><th class="tue">Tue</th><th class="wed">Wed</th><th class="thu">Thu</th><th class="fri">Fri</th><th class="sat">Sat</th><th class="sun">Sun</th></tr>
 <tr><td class="noday">&nbsp;</td><td class="noday">&nbsp;</td><td class="noday">&nbsp;</td><td class="thu">1</td><td class="fri">2</td><td class="sat">3</td><td class="sun">4</td></tr>
 <tr><td class="mon">5</td><td class="tue">6</td><td class="wed">7</td><td class="thu">8</td><td class="fri">9</td><td class="sat">10</td><td class="sun">11</td></tr>
@@ -104,8 +107,8 @@
 <tr><td class="mon">19</td><td class="tue">20</td><td class="wed">21</td><td class="thu">22</td><td class="fri">23</td><td class="sat">24</td><td class="sun">25</td></tr>
 <tr><td class="mon">26</td><td class="tue">27</td><td class="wed">28</td><td class="thu">29</td><td class="fri">30</td><td class="noday">&nbsp;</td><td class="noday">&nbsp;</td></tr>
 </table>
-</td><td><table border="0" cellpadding="0" cellspacing="0" class="month">
-<tr><th colspan="7" class="month">May</th></tr>
+</td><td><table border="0" cellpadding="0" cellspacing="0" class="{month}">
+<tr><th colspan="7" class="{month}">May</th></tr>
 <tr><th class="mon">Mon</th><th class="tue">Tue</th><th class="wed">Wed</th><th class="thu">Thu</th><th class="fri">Fri</th><th class="sat">Sat</th><th class="sun">Sun</th></tr>
 <tr><td class="noday">&nbsp;</td><td class="noday">&nbsp;</td><td class="noday">&nbsp;</td><td class="noday">&nbsp;</td><td class="noday">&nbsp;</td><td class="sat">1</td><td class="sun">2</td></tr>
 <tr><td class="mon">3</td><td class="tue">4</td><td class="wed">5</td><td class="thu">6</td><td class="fri">7</td><td class="sat">8</td><td class="sun">9</td></tr>
@@ -114,8 +117,8 @@
 <tr><td class="mon">24</td><td class="tue">25</td><td class="wed">26</td><td class="thu">27</td><td class="fri">28</td><td class="sat">29</td><td class="sun">30</td></tr>
 <tr><td class="mon">31</td><td class="noday">&nbsp;</td><td class="noday">&nbsp;</td><td class="noday">&nbsp;</td><td class="noday">&nbsp;</td><td class="noday">&nbsp;</td><td class="noday">&nbsp;</td></tr>
 </table>
-</td><td><table border="0" cellpadding="0" cellspacing="0" class="month">
-<tr><th colspan="7" class="month">June</th></tr>
+</td><td><table border="0" cellpadding="0" cellspacing="0" class="{month}">
+<tr><th colspan="7" class="{month}">June</th></tr>
 <tr><th class="mon">Mon</th><th class="tue">Tue</th><th class="wed">Wed</th><th class="thu">Thu</th><th class="fri">Fri</th><th class="sat">Sat</th><th class="sun">Sun</th></tr>
 <tr><td class="noday">&nbsp;</td><td class="tue">1</td><td class="wed">2</td><td class="thu">3</td><td class="fri">4</td><td class="sat">5</td><td class="sun">6</td></tr>
 <tr><td class="mon">7</td><td class="tue">8</td><td class="wed">9</td><td class="thu">10</td><td class="fri">11</td><td class="sat">12</td><td class="sun">13</td></tr>
@@ -123,8 +126,8 @@
 <tr><td class="mon">21</td><td class="tue">22</td><td class="wed">23</td><td class="thu">24</td><td class="fri">25</td><td class="sat">26</td><td class="sun">27</td></tr>
 <tr><td class="mon">28</td><td class="tue">29</td><td class="wed">30</td><td class="noday">&nbsp;</td><td class="noday">&nbsp;</td><td class="noday">&nbsp;</td><td class="noday">&nbsp;</td></tr>
 </table>
-</td></tr><tr><td><table border="0" cellpadding="0" cellspacing="0" class="month">
-<tr><th colspan="7" class="month">July</th></tr>
+</td></tr><tr><td><table border="0" cellpadding="0" cellspacing="0" class="{month}">
+<tr><th colspan="7" class="{month}">July</th></tr>
 <tr><th class="mon">Mon</th><th class="tue">Tue</th><th class="wed">Wed</th><th class="thu">Thu</th><th class="fri">Fri</th><th class="sat">Sat</th><th class="sun">Sun</th></tr>
 <tr><td class="noday">&nbsp;</td><td class="noday">&nbsp;</td><td class="noday">&nbsp;</td><td class="thu">1</td><td class="fri">2</td><td class="sat">3</td><td class="sun">4</td></tr>
 <tr><td class="mon">5</td><td class="tue">6</td><td class="wed">7</td><td class="thu">8</td><td class="fri">9</td><td class="sat">10</td><td class="sun">11</td></tr>
@@ -132,8 +135,8 @@
 <tr><td class="mon">19</td><td class="tue">20</td><td class="wed">21</td><td class="thu">22</td><td class="fri">23</td><td class="sat">24</td><td class="sun">25</td></tr>
 <tr><td class="mon">26</td><td class="tue">27</td><td class="wed">28</td><td class="thu">29</td><td class="fri">30</td><td class="sat">31</td><td class="noday">&nbsp;</td></tr>
 </table>
-</td><td><table border="0" cellpadding="0" cellspacing="0" class="month">
-<tr><th colspan="7" class="month">August</th></tr>
+</td><td><table border="0" cellpadding="0" cellspacing="0" class="{month}">
+<tr><th colspan="7" class="{month}">August</th></tr>
 <tr><th class="mon">Mon</th><th class="tue">Tue</th><th class="wed">Wed</th><th class="thu">Thu</th><th class="fri">Fri</th><th class="sat">Sat</th><th class="sun">Sun</th></tr>
 <tr><td class="noday">&nbsp;</td><td class="noday">&nbsp;</td><td class="noday">&nbsp;</td><td class="noday">&nbsp;</td><td class="noday">&nbsp;</td><td class="noday">&nbsp;</td><td class="sun">1</td></tr>
 <tr><td class="mon">2</td><td class="tue">3</td><td class="wed">4</td><td class="thu">5</td><td class="fri">6</td><td class="sat">7</td><td class="sun">8</td></tr>
@@ -142,8 +145,8 @@
 <tr><td class="mon">23</td><td class="tue">24</td><td class="wed">25</td><td class="thu">26</td><td class="fri">27</td><td class="sat">28</td><td class="sun">29</td></tr>
 <tr><td class="mon">30</td><td class="tue">31</td><td class="noday">&nbsp;</td><td class="noday">&nbsp;</td><td class="noday">&nbsp;</td><td class="noday">&nbsp;</td><td class="noday">&nbsp;</td></tr>
 </table>
-</td><td><table border="0" cellpadding="0" cellspacing="0" class="month">
-<tr><th colspan="7" class="month">September</th></tr>
+</td><td><table border="0" cellpadding="0" cellspacing="0" class="{month}">
+<tr><th colspan="7" class="{month}">September</th></tr>
 <tr><th class="mon">Mon</th><th class="tue">Tue</th><th class="wed">Wed</th><th class="thu">Thu</th><th class="fri">Fri</th><th class="sat">Sat</th><th class="sun">Sun</th></tr>
 <tr><td class="noday">&nbsp;</td><td class="noday">&nbsp;</td><td class="wed">1</td><td class="thu">2</td><td class="fri">3</td><td class="sat">4</td><td class="sun">5</td></tr>
 <tr><td class="mon">6</td><td class="tue">7</td><td class="wed">8</td><td class="thu">9</td><td class="fri">10</td><td class="sat">11</td><td class="sun">12</td></tr>
@@ -151,8 +154,8 @@
 <tr><td class="mon">20</td><td class="tue">21</td><td class="wed">22</td><td class="thu">23</td><td class="fri">24</td><td class="sat">25</td><td class="sun">26</td></tr>
 <tr><td class="mon">27</td><td class="tue">28</td><td class="wed">29</td><td class="thu">30</td><td class="noday">&nbsp;</td><td class="noday">&nbsp;</td><td class="noday">&nbsp;</td></tr>
 </table>
-</td></tr><tr><td><table border="0" cellpadding="0" cellspacing="0" class="month">
-<tr><th colspan="7" class="month">October</th></tr>
+</td></tr><tr><td><table border="0" cellpadding="0" cellspacing="0" class="{month}">
+<tr><th colspan="7" class="{month}">October</th></tr>
 <tr><th class="mon">Mon</th><th class="tue">Tue</th><th class="wed">Wed</th><th class="thu">Thu</th><th class="fri">Fri</th><th class="sat">Sat</th><th class="sun">Sun</th></tr>
 <tr><td class="noday">&nbsp;</td><td class="noday">&nbsp;</td><td class="noday">&nbsp;</td><td class="noday">&nbsp;</td><td class="fri">1</td><td class="sat">2</td><td class="sun">3</td></tr>
 <tr><td class="mon">4</td><td class="tue">5</td><td class="wed">6</td><td class="thu">7</td><td class="fri">8</td><td class="sat">9</td><td class="sun">10</td></tr>
@@ -160,8 +163,8 @@
 <tr><td class="mon">18</td><td class="tue">19</td><td class="wed">20</td><td class="thu">21</td><td class="fri">22</td><td class="sat">23</td><td class="sun">24</td></tr>
 <tr><td class="mon">25</td><td class="tue">26</td><td class="wed">27</td><td class="thu">28</td><td class="fri">29</td><td class="sat">30</td><td class="sun">31</td></tr>
 </table>
-</td><td><table border="0" cellpadding="0" cellspacing="0" class="month">
-<tr><th colspan="7" class="month">November</th></tr>
+</td><td><table border="0" cellpadding="0" cellspacing="0" class="{month}">
+<tr><th colspan="7" class="{month}">November</th></tr>
 <tr><th class="mon">Mon</th><th class="tue">Tue</th><th class="wed">Wed</th><th class="thu">Thu</th><th class="fri">Fri</th><th class="sat">Sat</th><th class="sun">Sun</th></tr>
 <tr><td class="mon">1</td><td class="tue">2</td><td class="wed">3</td><td class="thu">4</td><td class="fri">5</td><td class="sat">6</td><td class="sun">7</td></tr>
 <tr><td class="mon">8</td><td class="tue">9</td><td class="wed">10</td><td class="thu">11</td><td class="fri">12</td><td class="sat">13</td><td class="sun">14</td></tr>
@@ -169,8 +172,8 @@
 <tr><td class="mon">22</td><td class="tue">23</td><td class="wed">24</td><td class="thu">25</td><td class="fri">26</td><td class="sat">27</td><td class="sun">28</td></tr>
 <tr><td class="mon">29</td><td class="tue">30</td><td class="noday">&nbsp;</td><td class="noday">&nbsp;</td><td class="noday">&nbsp;</td><td class="noday">&nbsp;</td><td class="noday">&nbsp;</td></tr>
 </table>
-</td><td><table border="0" cellpadding="0" cellspacing="0" class="month">
-<tr><th colspan="7" class="month">December</th></tr>
+</td><td><table border="0" cellpadding="0" cellspacing="0" class="{month}">
+<tr><th colspan="7" class="{month}">December</th></tr>
 <tr><th class="mon">Mon</th><th class="tue">Tue</th><th class="wed">Wed</th><th class="thu">Thu</th><th class="fri">Fri</th><th class="sat">Sat</th><th class="sun">Sun</th></tr>
 <tr><td class="noday">&nbsp;</td><td class="noday">&nbsp;</td><td class="wed">1</td><td class="thu">2</td><td class="fri">3</td><td class="sat">4</td><td class="sun">5</td></tr>
 <tr><td class="mon">6</td><td class="tue">7</td><td class="wed">8</td><td class="thu">9</td><td class="fri">10</td><td class="sat">11</td><td class="sun">12</td></tr>
@@ -327,9 +330,12 @@ def neitherspacenordigit(c):
 
     def check_htmlcalendar_encoding(self, req, res):
         cal = calendar.HTMLCalendar()
+        format_ = default_format.copy()
+        format_["encoding"] = req or 'utf-8'
+        output = cal.formatyearpage(2004, encoding=req)
         self.assertEqual(
-            cal.formatyearpage(2004, encoding=req),
-            (result_2004_html % {'e': res}).encode(res)
+            output,
+            result_2004_html.format(**format_).encode(res)
         )
 
     def test_output(self):
@@ -825,7 +831,7 @@ def test_html_output_current_year(self):
     def test_html_output_year_encoding(self):
         stdout = self.run_ok('-t', 'html', '--encoding', 'ascii', '2004')
         self.assertEqual(stdout,
-                         (result_2004_html % {'e': 'ascii'}).encode('ascii'))
+                         result_2004_html.format(**default_format).encode('ascii'))
 
     def test_html_output_year_css(self):
         self.assertFailure('-t', 'html', '-c')
@@ -844,5 +850,47 @@ def test__all__(self):
         support.check__all__(self, calendar, blacklist=blacklist)
 
 
+class TestSubClassingCase(unittest.TestCase):
+
+    def setUp(self):
+
+        class CustomHTMLCal(calendar.HTMLCalendar):
+            cssclasses = [style + " text-nowrap" for style in
+                          calendar.HTMLCalendar.cssclasses]
+            cssclasses_weekday_head = ["red", "blue", "green", "lilac",
+                                       "yellow", "orange", "pink"]
+            cssclass_month_head = "text-center month-head"
+            cssclass_month = "text-center month"
+            cssclass_year = "text-italic "
+            cssclass_year_head = "lead "
+
+        self.cal = CustomHTMLCal()
+
+    def test_formatmonthname(self):
+        self.assertIn('class="text-center month-head"',
+                      self.cal.formatmonthname(2017, 5))
+
+    def test_formatmonth(self):
+        self.assertIn('class="text-center month"',
+                      self.cal.formatmonth(2017, 5))
+
+    def test_formatweek(self):
+        weeks = self.cal.monthdays2calendar(2017, 5)
+        self.assertIn('class="wed text-nowrap"', self.cal.formatweek(weeks[0]))
+
+    def test_formatweek_head(self):
+        header = self.cal.formatweekheader()
+        for color in self.cal.cssclasses_weekday_head:
+            self.assertIn('<th class="%s">' % color, header)
+
+    def test_format_year(self):
+        self.assertIn(
+            ('<table border="0" cellpadding="0" cellspacing="0" class="%s">' %
+             self.cal.cssclass_year), self.cal.formatyear(2017))
+
+    def test_format_year_head(self):
+        self.assertIn('<tr><th colspan="%d" class="%s">%s</th></tr>' % (
+            3, self.cal.cssclass_year_head, 2017), self.cal.formatyear(2017))
+
 if __name__ == "__main__":
     unittest.main()
diff --git a/Misc/ACKS b/Misc/ACKS
index 3000bc36d2c..85d2fc65c47 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -1556,6 +1556,7 @@ Jeremy Thurgood
 Eric Tiedemann
 July Tikhonov
 Tracy Tims
+Oz Tiram
 Oren Tirosh
 Tim Tisdall
 Jason Tishler