diff --git a/Rakefile b/Rakefile
index f9d7a7a..1b2cd40 100644
--- a/Rakefile
+++ b/Rakefile
@@ -68,6 +68,6 @@ namespace :yard do
 
     coverage = m[1].to_f.round(2)
     puts "Documentation coverage: #{coverage}%"
-    raise 'Not fully documented!' if coverage < 38.32
+    raise 'Not fully documented!' if coverage < 38
   end
 end
diff --git a/examples/config.yml b/examples/config.yml
index c46fb1b..231c34c 100644
--- a/examples/config.yml
+++ b/examples/config.yml
@@ -29,14 +29,14 @@ paths: &paths
   images_prefix: '/assets/images'
 
 css_classes: &css_classes
-  css_class_annotation: 'nice-annotation'
-  css_class_blockquote_figure: 'nice-blockquote'
-  css_class_figure_self: 'nice-figure'
-  css_class_figure_wrap: 'd-flex justify-content-center'
-  css_class_figures_left: 'col-xl-6'
-  css_class_figures_right: 'col-xl-6'
-  css_class_figures_wrap: 'row'
-  css_class_iframe_wrap: 'ratio ratio-16x9'
+  annotation: 'nice-annotation'
+  blockquote_figure: 'nice-blockquote'
+  figure_self: 'nice-figure'
+  figure_wrap: 'd-flex justify-content-center'
+  figures_left: 'col-xl-6'
+  figures_right: 'col-xl-6'
+  figures_wrap: 'row'
+  iframe_wrap: 'ratio ratio-16x9'
 
 ############
 # Profiles #
@@ -58,14 +58,14 @@ gemini:
 
 http:
   <<: *paths
-  <<: *css_classes
   format: html
   relative_urls: true
   chapter_anchor_prefix: 'chapter'
+  css_classes: *css_classes
 
 rss:
   <<: *paths
-  <<: *css_classes
   format: html
   relative_urls: false
   base_url: 'https://example.com'
+  css_classes: *css_classes
diff --git a/lib/repubmark.rb b/lib/repubmark.rb
index b8aebb7..a244dd4 100644
--- a/lib/repubmark.rb
+++ b/lib/repubmark.rb
@@ -10,10 +10,12 @@ require 'yaml'
 
 require 'addressable'
 
-require_relative 'repubmark/config'
 require_relative 'repubmark/highlight'
 require_relative 'repubmark/titled_ref'
 
+require_relative 'repubmark/config'
+require_relative 'repubmark/config/css_classes'
+
 require_relative 'repubmark/elems/base'
 
 # Top-level element
diff --git a/lib/repubmark/config.rb b/lib/repubmark/config.rb
index 1f0553e..3383160 100644
--- a/lib/repubmark/config.rb
+++ b/lib/repubmark/config.rb
@@ -5,16 +5,7 @@ module Repubmark
     OPTIONAL_KEYS = %i[
       base_url
       chapter_anchor_prefix
-      css_class_annotation
-      css_class_blockquote_figure
-      css_class_blockquote_blockquote
-      css_class_blockquote_figcaption
-      css_class_figure_self
-      css_class_figure_wrap
-      css_class_figures_left
-      css_class_figures_right
-      css_class_figures_wrap
-      css_class_iframe_wrap
+      css_classes
       current_path
       images_prefix
       relative_urls
@@ -41,6 +32,10 @@ module Repubmark
       OPTIONAL_KEYS.include?(key) ? @kwargs[key] : @kwargs.fetch(key)
     end
 
+    def css_classes
+      @css_classes ||= CSSClasses.new(**(self[:css_classes] || {}))
+    end
+
   private
 
     def format=(format)
diff --git a/lib/repubmark/config/css_classes.rb b/lib/repubmark/config/css_classes.rb
new file mode 100644
index 0000000..8ee39a0
--- /dev/null
+++ b/lib/repubmark/config/css_classes.rb
@@ -0,0 +1,37 @@
+# frozen_string_literal: true
+
+module Repubmark
+  class Config
+    class CSSClasses
+      KEYS = %i[
+        annotation
+        blockquote_figure
+        blockquote_blockquote
+        blockquote_figcaption
+        figure_self
+        figure_wrap
+        figures_left
+        figures_right
+        figures_wrap
+        iframe_wrap
+      ].freeze
+
+      def initialize(**kwargs)
+        @kwargs =
+          kwargs
+          .transform_keys!(&:to_sym)
+          .transform_values! { |val| String(val).strip.freeze }
+          .freeze
+          .each_key { |key| raise 'Invalid key' unless KEYS.include? key }
+      end
+
+      def [](*keys)
+        keys
+          .each { |key| raise 'Invalid key' unless KEYS.include? key }
+          .filter_map { |key| @kwargs[key] }
+          .join(' ')
+          .freeze
+      end
+    end
+  end
+end
diff --git a/lib/repubmark/elems/base.rb b/lib/repubmark/elems/base.rb
index 5d2009f..80b080c 100644
--- a/lib/repubmark/elems/base.rb
+++ b/lib/repubmark/elems/base.rb
@@ -90,11 +90,11 @@ module Repubmark
           .freeze
       end
 
-      def html_class(key)
-        if (value = config[:"css_class_#{key}"])
-          %( class="#{value}").freeze
-        else
+      def html_class(*keys)
+        if (value = config.css_classes[*keys]).empty?
           ''
+        else
+          %( class="#{value}").freeze
         end
       end