diff --git a/_config.yml b/_config.yml
index 20bf8a1..aca049e 100644
--- a/_config.yml
+++ b/_config.yml
@@ -99,6 +99,11 @@ ga_tracking_anonymize_ip: true # Use GDPR compliant Google Analytics settings (t
 plugins:
   - jekyll-seo-tag
 
+kramdown:
+  syntax_highlighter_opts:
+    block:
+      line_numbers: false
+
 compress_html:
   clippings: all
   comments: all
@@ -106,3 +111,5 @@ compress_html:
   startings: []
   blanklines: false
   profile: false
+  # ignore:
+  #   envs: all
diff --git a/_includes/fix_linenos.html b/_includes/fix_linenos.html
new file mode 100644
index 0000000..6243fb0
--- /dev/null
+++ b/_includes/fix_linenos.html
@@ -0,0 +1,65 @@
+{%- comment -%}
+This file can be used to fix the HTML produced by Jekyll for highlighted
+code with line numbers.
+
+It works with `{% highlight some_language linenos %}...{% endhighlight %}`
+and with the Kramdown option to add line numbers to fenced code.
+
+The implementation was derived from the workaround provided by 
+Dmitry Hrabrov (DeXP) at
+https://github.com/penibelst/jekyll-compress-html/issues/71#issuecomment-188144901
+
+EXPLANATION
+
+The HTML produced by Rouge highlighting with lie numbers is of the form
+`code table`. Jekyll (<= 4.1.1) always wraps the highlighted HTML
+with `pre`. This wrapping is not only unnecessary, but also transforms
+the conforming HTML produced by Rouge to non-conforming HTML, which
+results in HTML validation error reports. 
+
+The fix removes the outer `pre` tags whenever they contain the pattern
+`<table class="rouge-table">`.
+  
+Apart from avoiding HTML validation errors, the fix allows the use of
+the [Jekyll layout for compressing HTML](http://jch.penibelst.de),
+which relies on `pre` tags not being nested, according to
+https://github.com/penibelst/jekyll-compress-html/issues/71#issuecomment-172069842 
+
+USAGE
+
+(Any names can be used for `some_var` and `some_language`.)
+
+{% capture some_var %}
+{% highlight some_language linenos %}
+Some code
+{% endhighlight %}
+{% endcapture %}
+{% include fix_linenos.html code=some_var %}
+
+For code fences:
+
+{% capture some_var %}
+```some_language
+Some code
+```
+{% endcapture %}
+{% assign some_var = some_var | markdownify %}
+{% include fix_linenos.html code=some_var %}
+
+CAVEATS
+
+The above does not work when `Some code` happens to contain the matched string 
+`<table class="rouge-table">`.
+
+The use of this file overwrites the variable `fix_linenos_code` with `nil`.
+
+{%- endcomment -%}
+
+{% assign fix_linenos_code = include.code %}
+{% if fix_linenos_code contains '<table class="rouge-table">' %}
+  {% assign fix_linenos_code = fix_linenos_code | replace: '<pre class="highlight">', '<pre>' %}
+  {% assign fix_linenos_code = fix_linenos_code | replace: "<pre><code", "<code" %}
+  {% assign fix_linenos_code = fix_linenos_code | replace: "</code></pre>", "</code>" %}
+{% endif %}
+{{ fix_linenos_code }}
+{% assign fix_linenos_code = nil %}
diff --git a/_sass/code.scss b/_sass/code.scss
index affc8aa..ead2c5f 100644
--- a/_sass/code.scss
+++ b/_sass/code.scss
@@ -11,23 +11,96 @@ code {
   border-radius: $border-radius;
 }
 
-pre.highlight,
-figure.highlight {
+// Content structure for highlighted code blocks using fences or Liquid
+//
+// ```[LANG]...```, no kramdown line_numbers:
+//   div.[language-LANG.]highlighter-rouge > div.highlight > pre.highlight > code
+//
+// ```[LANG]...```, kramdown line_numbers = true:
+//   div.[language-LANG.]highlighter-rouge > div.highlight > pre.highlight > code
+//   > div.table-wrapper > table.rouge-table > tbody > tr
+//   > td.rouge-gutter.gl > pre.lineno
+//   | td.rouge-code > pre
+//
+// {% highlight LANG %}...{% endhighlight %}:
+//   figure.highlight > pre > code.language-LANG
+//
+// {% highlight LANG linenos %}...{% endhighlight %}:
+//   figure.highlight > pre > code.language-LANG
+//   > div.table-wrapper > table.rouge-table > tbody > tr
+//   > td.gutter.gl > pre.lineno
+//   | td.code > pre
+//
+// fix_linenos removes the outermost pre when it encloses table.rouge-table
+//
+// See docs/index-test.md for some tests.
+//
+// No kramdown line_numbers: fences and Liquid highlighting look the same.
+// Kramdown line_numbers = true: fences have a wider gutter than with Liquid?
+
+// ```[LANG]...```
+div.highlighter-rouge {
   padding: $sp-3;
   margin-top: 0;
-  margin-bottom: 0;
+  margin-bottom: $sp-3;
   background-color: $code-background-color;
   border-radius: $border-radius;
+  box-shadow: none;
   -webkit-overflow-scrolling: touch;
 
+  div.highlight,
+  pre.highlight,
   code {
     padding: 0;
+    margin: 0;
     border: 0;
   }
 }
 
-.highlighter-rouge {
+// {% highlight LANG %}...{% endhighlight %},
+// {% highlight LANG linenos %}...{% endhighlight %}:
+figure.highlight {
+  padding: $sp-3;
+  margin-top: 0;
   margin-bottom: $sp-3;
+  background-color: $code-background-color;
+  border-radius: $border-radius;
+  box-shadow: none;
+  -webkit-overflow-scrolling: touch;
+
+  pre,
+  code {
+    padding: 0;
+    margin: 0;
+    border: 0;
+  }
+}
+
+// ```[LANG]...```, kramdown line_numbers = true,
+// {% highlight LANG linenos %}...{% endhighlight %}:
+.highlight .table-wrapper {
+  padding: 0;
+  margin: 0;
+  border: 0;
+  box-shadow: none;
+
+  td,
+  pre {
+    @include fs-2;
+    min-width: 0;
+    padding: 0;
+    background-color: $code-background-color;
+    border: 0;
+  }
+
+  td.gl {
+    padding-right: $sp-3;
+  }
+
+  pre {
+    margin: 0;
+    line-height: 2;
+  }
 }
 
 .highlight .c {
diff --git a/docs/ui-components/code.md b/docs/ui-components/code.md
index e53a90d..b8136a3 100644
--- a/docs/ui-components/code.md
+++ b/docs/ui-components/code.md
@@ -2,6 +2,7 @@
 layout: default
 title: Code
 parent: UI Components
+has_children: true
 nav_order: 6
 ---
 
diff --git a/docs/ui-components/linenos.md b/docs/ui-components/linenos.md
new file mode 100644
index 0000000..b13e6c9
--- /dev/null
+++ b/docs/ui-components/linenos.md
@@ -0,0 +1,124 @@
+---
+layout: default
+title: Code with line numbers
+parent: Code
+grand_parent: UI Components
+---
+
+# Configuration options
+
+The default settings for HTML compression are incompatible with the HTML
+produced by Jekyll (4.1.1 or earlier) for line numbers from highlighted code
+-- both when using Kramdown code fences and when using Liquid highlight tags.
+
+To avoid non-conforming HTML and unsatisfactory layout, HTML compression
+can be turned off by using the following configuration option:
+
+{% highlight yaml %}
+compress_html:
+  ignore:
+    envs: all
+{% endhighlight %}
+
+When using Kramdown code fences, line numbers are turned on globally by the
+following configuration option:
+
+{% highlight yaml %}
+kramdown:
+  syntax_highlighter_opts:
+    block:
+      line_numbers: false
+{% endhighlight %}
+
+Line numbers can then be suppressed locally using Liquid tags (_without_ the
+`linenos` option) instead of fences:
+
+{% highlight yaml %}
+{% raw %}{% highlight some_language %}
+Some code
+{% endhighlight %}{% endraw %}
+{% endhighlight %}
+
+# Workarounds
+
+To use HTML compression together with line numbers, all highlighted code
+needs to be wrapped using one of the following workarounds.
+(The variable name `some_var` can be changed to avoid clashes; it can also
+be replaced by `code` -- but note that `code=code` cannot be removed).
+
+## Code fences
+
+{% highlight default %}
+{% raw %}{% capture some_var %}
+```some_language
+Some code
+```
+{% endcapture %}
+{% assign some_var = some_var | markdownify %}
+{% include fix_linenos.html code=some_var %}{% endraw %}
+{% endhighlight %}
+
+## Liquid highlighting
+
+{% highlight default %}
+{% raw %}{% capture some_var %}
+{% highlight some_language linenos %}
+Some code
+{% endhighlight %}
+{% endcapture %}
+{% include fix_linenos.html code=some_var %}{% endraw %}
+{% endhighlight %}
+
+_Credit:_ The original version of the above workaround was suggested by
+Dmitry Hrabrov at
+<https://github.com/penibelst/jekyll-compress-html/issues/71#issuecomment-188144901>.
+
+# Examples
+
+```
+Some unknown code in fences
+```
+
+```js
+// Javascript code with syntax highlighting in fences
+var fun = function lang(l) {
+  dateformat.i18n = require('./lang/' + l)
+  return true;
+}
+```
+
+```ruby
+# Ruby code with syntax highlighting in fences
+GitHubPages::Dependencies.gems.each do |gem, version|
+  s.add_dependency(gem, "= #{version}")
+end
+```
+
+{% highlight ruby %}
+# Ruby code with syntax highlighting using Liquid
+GitHubPages::Dependencies.gems.each do |gem, version|
+  s.add_dependency(gem, "= #{version}")
+end
+{% endhighlight %}
+
+{% capture code %}
+{% highlight ruby linenos %}
+# Ruby code with syntax highlighting and fixed line numbers using Liquid
+GitHubPages::Dependencies.gems.each do |gem, version|
+  s.add_dependency(gem, "= #{version}")
+end
+{% endhighlight %}
+{% endcapture %}
+{% include fix_linenos.html code=code %}
+{% assign code = nil %}
+
+With the default configuration options, the following example illustrates
+the incorrect formatting arising from the incompatibility of HTML compression
+and the non-conforming HTML produced by Jekyll for line numbers:
+
+{% highlight ruby linenos %}
+# Ruby code with syntax highlighting and unfixed line numbers using Liquid
+GitHubPages::Dependencies.gems.each do |gem, version|
+  s.add_dependency(gem, "= #{version}")
+end
+{% endhighlight %}