diff --git a/app/Controllers/Findingaid.php b/app/Controllers/Findingaid.php
index 61e140f..7e6a2a5 100644
--- a/app/Controllers/Findingaid.php
+++ b/app/Controllers/Findingaid.php
@@ -32,6 +32,11 @@ public function show()
             return;
         }
 
+        $css = [
+            'extra_version' => $this->assetVersion('css/extra.css'),
+            'mediaelementplayer_version' => $this->assetVersion('css/mediaelementplayer.min.css'),
+        ];
+
         /* First, fill out top-level metadata, including the
          * table of contents.
          */
@@ -305,17 +310,10 @@ public function show()
                     'content' => $content,
                     'toc' => $toc,
                     'requests' => $requests,
+                    'css' => $css,
                     'js' => [[
                         'href' => 'js/app.js',
-                        'hash' => hash_file('sha256', implode(
-                            DIRECTORY_SEPARATOR,
-                            [
-                                ROOT,
-                                'public',
-                                'js',
-                                'app.js',
-                            ]
-                        )),
+                        'version' => $this->assetVersion('js/app.js'),
                     ]],
                     'title' => $model->title(),
                     'requestable' => $requestable,
@@ -353,6 +351,7 @@ public function show()
                         [
                             'title' => $meta['title'],
                             'repository' => $meta['repository'],
+                            'css' => $css,
                         ]
                     );
                 } else {
@@ -362,6 +361,7 @@ public function show()
                             'title' => $meta['title'],
                             'repository' => $meta['repository'],
                             'repo_url' => $repo_url,
+                            'css' => $css,
                         ]
                     );
                 }
diff --git a/app/Core/Controller.php b/app/Core/Controller.php
index 4373916..15b5369 100644
--- a/app/Core/Controller.php
+++ b/app/Core/Controller.php
@@ -11,4 +11,16 @@ public function __construct(protected $params = [])
         global $g_config;
         $this->config = $g_config;
     }
+
+    public function assetVersion($path)
+    {
+        $file_path = implode(DIRECTORY_SEPARATOR, [
+            realpath(ROOT),
+            'public',
+            $path,
+        ]);
+        $algo = 'sha384';
+        $version = $algo . '-' . base64_encode(hash($algo, file_get_contents($file_path), true));
+        return $version;
+    }
 }
diff --git a/app/Views/Euk_Shared/head-common.mustache b/app/Views/Euk_Shared/head-common.mustache
index 4c034ee..ff81cea 100644
--- a/app/Views/Euk_Shared/head-common.mustache
+++ b/app/Views/Euk_Shared/head-common.mustache
@@ -8,8 +8,8 @@
     <link rel="preconnect" href="https://fonts.gstatic.com">
 
     <!--shared css-->
-    <link rel="stylesheet" href="css/extra.css">
-    <link rel="stylesheet" href="css/mediaelementplayer.min.css">
+    <link rel="stylesheet" href="css/extra.css?{{css.extra_version}}">
+    <link rel="stylesheet" href="css/mediaelementplayer.min.css?{{css.mediaelementplayer_version}}">
     <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/lity/2.3.1/lity.min.css" integrity="sha256-0SZxASYAglrmIuTx+ZYHE3hzTnCZWB7XLu+iA8AG0Z0=" crossorigin="anonymous" />
 
     <!--Limestone CSS -->
diff --git a/app/Views/Layouts/application.mustache b/app/Views/Layouts/application.mustache
index 0e1a3ef..44c6983 100644
--- a/app/Views/Layouts/application.mustache
+++ b/app/Views/Layouts/application.mustache
@@ -47,7 +47,7 @@
   {{> universal-footer}}
   {{> limestone-resources}}
   {{#js}}
-  <script src="{{href}}?hash={{hash}}"></script>
+  <script src="{{href}}?{{version}}"></script>
   {{/js}}
   {{#requestable}}
   <script>
diff --git a/tests/ControllerTest.php b/tests/ControllerTest.php
new file mode 100644
index 0000000..84c1cdf
--- /dev/null
+++ b/tests/ControllerTest.php
@@ -0,0 +1,22 @@
+<?php
+
+namespace Tests\Unit;
+
+use App\Core\Controller;
+use PHPUnit\Framework\TestCase;
+
+class ControllerTest extends TestCase
+{
+    public function testAssetVersionIsASha384DigestOfTheAssetContents(): void
+    {
+        $path = 'css/extra.css';
+        $contents = file_get_contents(implode(DIRECTORY_SEPARATOR, [
+            ROOT,
+            'public',
+            $path,
+        ]));
+        $expected = 'sha384-' . base64_encode(hash('sha384', $contents, true));
+
+        $this->assertSame($expected, (new Controller())->assetVersion($path));
+    }
+}