diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
new file mode 100644
index 0000000..093493f
--- /dev/null
+++ b/.github/workflows/build.yml
@@ -0,0 +1,33 @@
+name: Build
+
+on:
+  pull_request:
+  push:
+    branches: [main]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      # Reads Ruby version from .ruby-version and installs gems.
+      # bundler-cache: true runs bundle install (non-frozen) so it resolves the
+      # x86_64-linux platform that the darwin-only Gemfile.lock doesn't include.
+      - uses: ruby/setup-ruby@v1
+        with:
+          bundler-cache: true
+
+      # Reads Node version from .nvmrc (18) and caches Yarn downloads.
+      - uses: actions/setup-node@v4
+        with:
+          node-version-file: .nvmrc
+          cache: yarn
+
+      - run: yarn install --frozen-lockfile
+
+      # Exact command Netlify uses to publish the site (see netlify.toml).
+      # Plain `bundle exec jekyll build` fails — jekyll-postcss requires
+      # JEKYLL_ENV=production for a one-off build without the dev server.
+      - name: Build site
+        run: JEKYLL_ENV=production bundle exec jekyll build
diff --git a/Gemfile.lock b/Gemfile.lock
index aa2d97e..c309b0f 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -16,6 +16,7 @@ GEM
     execjs (2.9.1)
     ffi (1.17.2-arm64-darwin)
     ffi (1.17.2-x86_64-darwin)
+    ffi (1.17.2-x86_64-linux-gnu)
     forwardable-extended (2.6.0)
     google-protobuf (4.30.2-arm64-darwin)
       bigdecimal
@@ -23,6 +24,9 @@ GEM
     google-protobuf (4.30.2-x86_64-darwin)
       bigdecimal
       rake (>= 13)
+    google-protobuf (4.30.2-x86_64-linux)
+      bigdecimal
+      rake (>= 13)
     htmlcompressor (0.4.0)
     http_parser.rb (0.8.0)
     i18n (1.14.7)
@@ -87,6 +91,8 @@ GEM
       google-protobuf (~> 4.30)
     sass-embedded (1.87.0-x86_64-darwin)
       google-protobuf (~> 4.30)
+    sass-embedded (1.87.0-x86_64-linux-gnu)
+      google-protobuf (~> 4.30)
     terminal-table (3.0.2)
       unicode-display_width (>= 1.1.1, < 3)
     uglifier (4.2.0)
@@ -100,6 +106,7 @@ PLATFORMS
   arm64-darwin-24
   x86_64-darwin-21
   x86_64-darwin-23
+  x86_64-linux
 
 DEPENDENCIES
   http_parser.rb (~> 0.6.0)
@@ -114,4 +121,4 @@ DEPENDENCIES
   webrick (~> 1.7)
 
 BUNDLED WITH
-   2.3.22
+   2.5.22