diff --git a/README.md b/README.md
index 7b19348..0c4b93d 100644
--- a/README.md
+++ b/README.md
@@ -109,7 +109,6 @@ rake rubocop
 rake spec
 ```
 
-
 ## Licence
 
 AutoHtml is released under the [MIT License](https://raw.githubusercontent.com/dejan/auto_html/master/MIT-LICENSE).
diff --git a/demo/.ruby-version b/demo/.ruby-version
index 75a22a2..fa7adc7 100644
--- a/demo/.ruby-version
+++ b/demo/.ruby-version
@@ -1 +1 @@
-3.0.3
+3.3.5
diff --git a/demo/Dockerfile b/demo/Dockerfile
index a070205..9666071 100644
--- a/demo/Dockerfile
+++ b/demo/Dockerfile
@@ -1,4 +1,4 @@
-FROM ruby:2.5-alpine
+FROM ruby:3.3-alpine
 
 RUN apk --update add \
       alpine-sdk && \
diff --git a/demo/Gemfile b/demo/Gemfile
index 84c7b4e..cf973f4 100644
--- a/demo/Gemfile
+++ b/demo/Gemfile
@@ -5,6 +5,7 @@ source 'https://rubygems.org'
 gem 'auto_html'
 gem 'puma'
 gem 'rack-test'
+gem 'rackup'
 gem 'rerun'
 gem 'roda'
 gem 'rspec'
diff --git a/demo/Gemfile.lock b/demo/Gemfile.lock
index d5ede94..bd5bcd8 100644
--- a/demo/Gemfile.lock
+++ b/demo/Gemfile.lock
@@ -7,60 +7,72 @@ GEM
       redcarpet (~> 3.5)
       rexml (~> 3.2.5)
       rinku (~> 2.0)
-    diff-lcs (1.4.4)
-    ffi (1.15.4)
-    gemoji (4.0.0.rc3)
-    listen (3.7.0)
+    diff-lcs (1.5.1)
+    ffi (1.17.1-x86_64-darwin)
+    ffi (1.17.1-x86_64-linux-gnu)
+    gemoji (4.0.1)
+    json (2.9.1)
+    language_server-protocol (3.17.0.3)
+    listen (3.9.0)
       rb-fsevent (~> 0.10, >= 0.10.3)
       rb-inotify (~> 0.9, >= 0.9.10)
-    nio4r (2.7.3)
-    parallel (1.21.0)
-    parser (3.0.3.1)
+    nio4r (2.7.4)
+    parallel (1.26.3)
+    parser (3.3.6.0)
       ast (~> 2.4.1)
-    puma (5.6.9)
+      racc
+    puma (6.5.0)
       nio4r (~> 2.0)
-    rack (2.2.8.1)
-    rack-test (1.1.0)
-      rack (>= 1.0, < 3)
-    rainbow (3.0.0)
-    rb-fsevent (0.11.0)
-    rb-inotify (0.10.1)
+    racc (1.8.1)
+    rack (3.1.8)
+    rack-test (2.2.0)
+      rack (>= 1.3)
+    rackup (2.2.1)
+      rack (>= 3)
+    rainbow (3.1.1)
+    rb-fsevent (0.11.2)
+    rb-inotify (0.11.1)
       ffi (~> 1.0)
-    redcarpet (3.5.1)
-    regexp_parser (2.1.1)
-    rerun (0.13.1)
+    redcarpet (3.6.0)
+    regexp_parser (2.10.0)
+    rerun (0.14.0)
       listen (~> 3.0)
-    rexml (3.2.5)
+    rexml (3.2.9)
+      strscan
     rinku (2.0.6)
-    roda (3.50.0)
+    roda (3.87.0)
       rack
-    rspec (3.10.0)
-      rspec-core (~> 3.10.0)
-      rspec-expectations (~> 3.10.0)
-      rspec-mocks (~> 3.10.0)
-    rspec-core (3.10.1)
-      rspec-support (~> 3.10.0)
-    rspec-expectations (3.10.1)
+    rspec (3.13.0)
+      rspec-core (~> 3.13.0)
+      rspec-expectations (~> 3.13.0)
+      rspec-mocks (~> 3.13.0)
+    rspec-core (3.13.2)
+      rspec-support (~> 3.13.0)
+    rspec-expectations (3.13.3)
       diff-lcs (>= 1.2.0, < 2.0)
-      rspec-support (~> 3.10.0)
-    rspec-mocks (3.10.2)
+      rspec-support (~> 3.13.0)
+    rspec-mocks (3.13.2)
       diff-lcs (>= 1.2.0, < 2.0)
-      rspec-support (~> 3.10.0)
-    rspec-support (3.10.3)
-    rubocop (1.23.0)
+      rspec-support (~> 3.13.0)
+    rspec-support (3.13.2)
+    rubocop (1.69.2)
+      json (~> 2.3)
+      language_server-protocol (>= 3.17.0)
       parallel (~> 1.10)
-      parser (>= 3.0.0.0)
+      parser (>= 3.3.0.2)
       rainbow (>= 2.2.2, < 4.0)
-      regexp_parser (>= 1.8, < 3.0)
-      rexml
-      rubocop-ast (>= 1.12.0, < 2.0)
+      regexp_parser (>= 2.9.3, < 3.0)
+      rubocop-ast (>= 1.36.2, < 2.0)
       ruby-progressbar (~> 1.7)
-      unicode-display_width (>= 1.4.0, < 3.0)
-    rubocop-ast (1.14.0)
-      parser (>= 3.0.1.1)
-    ruby-progressbar (1.11.0)
-    tilt (2.0.10)
-    unicode-display_width (2.1.0)
+      unicode-display_width (>= 2.4.0, < 4.0)
+    rubocop-ast (1.37.0)
+      parser (>= 3.3.1.0)
+    ruby-progressbar (1.13.0)
+    strscan (3.1.2)
+    tilt (2.5.0)
+    unicode-display_width (3.1.3)
+      unicode-emoji (~> 4.0, >= 4.0.4)
+    unicode-emoji (4.0.4)
 
 PLATFORMS
   x86_64-darwin-19
@@ -70,6 +82,7 @@ DEPENDENCIES
   auto_html
   puma
   rack-test
+  rackup
   rerun
   roda
   rspec