diff --git a/.forgejo/workflows/deploy.yaml b/.forgejo/workflows/deploy.yaml
index b08a439..cb9ff00 100644
--- a/.forgejo/workflows/deploy.yaml
+++ b/.forgejo/workflows/deploy.yaml
@@ -13,7 +13,7 @@ jobs:
   build:
     runs-on: docker
     container:
-      image: hugomods/hugo:exts-0.148.1
+      image: hugomods/hugo:dart-sass-0.158.0
     steps:
       - name: Pipeline info
         run: |
diff --git a/README.md b/README.md
index 8bf8426..ce34ab0 100644
--- a/README.md
+++ b/README.md
@@ -34,6 +34,8 @@ Please note, that the website should be re-deployed at least daily to update the
 ### Add Pages
 
 To run a local version, just install HUGO by following the [instructions](https://gohugo.io/installation/) for your operating system.
+Note that you also need to install the [Dart Sass compiler](https://sass-lang.com/dart-sass/).
+
 To build the website and run a development webserver, execute:
 ```shell
 hugo server
diff --git a/hugo.toml b/hugo.toml
index 3b2548b..62fb6ad 100644
--- a/hugo.toml
+++ b/hugo.toml
@@ -1,5 +1,5 @@
 baseURL = 'https://hamburg.ccc.de/'
-languageCode = 'de-de'
+locale = 'de-de'
 defaultContentLanguage = 'de'
 timeZone = 'Europe/Berlin'
 title = 'CCC Hansestadt Hamburg e.V.'
diff --git a/themes/ccchh/assets/sass/main.scss b/themes/ccchh/assets/sass/main.scss
index 0396a7e..9784806 100644
--- a/themes/ccchh/assets/sass/main.scss
+++ b/themes/ccchh/assets/sass/main.scss
@@ -1,3 +1,6 @@
+@use "sass:map";
+@use "sass:math";
+
 $roomstate_color_unknown: #dda218;
 $roomstate_color_open: var(--ins-color);
 $roomstate_color_closed: var(--del-color);
@@ -164,7 +167,12 @@ body>main {
     margin-bottom: 1rem;
   }
 
-  h1, h2, h3, h4, h5, h6 {
+  h1,
+  h2,
+  h3,
+  h4,
+  h5,
+  h6 {
     margin: 0.5rem 1rem;
   }
 
@@ -202,7 +210,7 @@ body>main {
       display: block;
       margin: 0 auto;
       // (250px - 2*var(--grid-spacing-horizontal)) * 3/4
-      max-height: (222px * 3/4);
+      max-height: math.div(222px * 3, 4);
     }
 
     // 2*250px + 2*var(--spacing) + 1px
@@ -211,7 +219,7 @@ body>main {
 
       img.groups-img {
         // (150px - 2*var(--grid-spacing-horizontal)) * 3/4
-        max-height: (122px*3/4);
+        max-height: math.div(122px*3, 4);
       }
     }
 
@@ -221,7 +229,7 @@ body>main {
 
       img.groups-img {
         // (350px - 2*var(--grid-spacing-horizontal)) * 3/4
-        max-height: (322px*3/4);
+        max-height: math.div(322px*3, 4);
       }
 
       // 2*350px + 2*var(--spacing) + 1px
@@ -230,7 +238,7 @@ body>main {
 
         img.groups-img {
           // (250px - 2*var(--grid-spacing-horizontal)) * 3/4
-          max-height: (222px*3/4);
+          max-height: math.div(222px*3, 4);
         }
       }
     }
@@ -295,7 +303,7 @@ body>main {
   // When the header content doesn't display nicely anymore, switch to mobile mode.
   @import "../pico-1.5.11/scss/variables";
 
-  @media (max-width: map-get($breakpoints, md)) {
+  @media (max-width: map.get($breakpoints, md)) {
     .hamburger-button {
       display: unset;
       position: absolute;
@@ -375,15 +383,15 @@ body>main {
       }
 
       // Use the media queries, which we need, from here:
-      @if map-get($breakpoints, "sm") {
-        @media (min-width: map-get($breakpoints, "sm")) {
+      @if map.get($breakpoints, "sm") {
+        @media (min-width: map.get($breakpoints, "sm")) {
           ul {
             padding-left: 0;
             padding-right: 0;
           }
 
           .main-nav {
-            max-width: map-get($viewports, "sm");
+            max-width: map.get($viewports, "sm");
           }
         }
       }
diff --git a/themes/ccchh/layouts/_default/rss.xml b/themes/ccchh/layouts/_default/rss.xml
index f4a91aa..baf0f96 100644
--- a/themes/ccchh/layouts/_default/rss.xml
+++ b/themes/ccchh/layouts/_default/rss.xml
@@ -37,7 +37,7 @@
     <link>{{ .Permalink }}</link>
     <description>Recent content {{ if ne .Title .Site.Title }}{{ with .Title }}in {{ . }} {{ end }}{{ end }}on {{ .Site.Title }}</description>
     <generator>Hugo</generator>
-    <language>{{ site.Language.LanguageCode }}</language>{{ with $authorEmail }}
+    <language>{{ site.Language.Locale }}</language>{{ with $authorEmail }}
     <managingEditor>{{.}}{{ with $authorName }} ({{ . }}){{ end }}</managingEditor>{{ end }}{{ with $authorEmail }}
     <webMaster>{{ . }}{{ with $authorName }} ({{ . }}){{ end }}</webMaster>{{ end }}{{ with .Site.Copyright }}
     <copyright>{{ . }}</copyright>{{ end }}{{ if not .Date.IsZero }}
diff --git a/themes/ccchh/layouts/partials/head.html b/themes/ccchh/layouts/partials/head.html
index 936de41..22ed943 100644
--- a/themes/ccchh/layouts/partials/head.html
+++ b/themes/ccchh/layouts/partials/head.html
@@ -1,5 +1,5 @@
-{{- $cssOptionsMain := dict "transpiler" "libsass" "targetPath" "css/style.css" -}}
-{{- $cssOptionsPico := dict "transpiler" "libsass" "targetPath" "css/pico.css" -}}
+{{- $cssOptionsMain := dict "transpiler" "dartsass" "targetPath" "css/style.css" -}}
+{{- $cssOptionsPico := dict "transpiler" "dartsass" "targetPath" "css/pico.css" -}}
 {{- $jsResources := resources.Match "js/*.js" }}
 
   <meta name="viewport" content="width=device-width, initial-scale=1.0">
diff --git a/themes/ccchh/layouts/shortcodes/calendar-table.html b/themes/ccchh/layouts/shortcodes/calendar-table.html
index 558f824..c0c2cbb 100644
--- a/themes/ccchh/layouts/shortcodes/calendar-table.html
+++ b/themes/ccchh/layouts/shortcodes/calendar-table.html
@@ -1,4 +1,4 @@
-{{- index .Site.Data "calendar.json" }}
+{{- index hugo.Data "calendar.json" }}
 <table>
   <thead>
     <tr>
@@ -8,7 +8,7 @@
     </tr>
   </thead>
   <tbody>
-  {{- range first 7 (sort $.Site.Data.calendar "dtstart" ) }}
+  {{- range first 7 (sort hugo.Data.calendar "dtstart" ) }}
     {{- if eq ._type "vevent"}}
     <tr>
       {{- $start := time .dtstart }}