Standardize node.js requirements.

.github/workflows/build-css.yml

@@ -34,7 +34,8 @@ jobs:
 
       - name: Install dependencies
         run: |
-          npm install -g sass autoprefixer cssnano postcss postcss-cli
+          npm clean-install
+        working-directory: ./src/sphinx_antsibull_ext/css
 
       - name: Build CSS
         run: |

README.md

@@ -84,14 +84,10 @@ cd sphinx_antsibull_ext/css/
 ./build-css.sh
 ```
 
-For this to work, you need to make sure that `sassc` and `postcss` are on your path and that the autoprefixer and nanocss modules are installed:
+For this to work, you need to install some Node.js dependencies:
 
 ```console
-# Debian:
-apt-get install sassc
-
-# PostCSS, autoprefixer and cssnano require nodejs/npm:
-npm install -g autoprefixer cssnano postcss postcss-cli
+npm clean-install
 ```
 
 ## Creating a new release:

src/sphinx_antsibull_ext/css/.gitignore

@@ -0,0 +1,4 @@
+# Copyright (c) Ansible and contributors
+# GNU General Public License v3.0+ (see https://www.gnu.org/licenses/gpl-3.0.txt)
+
+/node_modules

src/sphinx_antsibull_ext/css/build.sh

@@ -3,16 +3,16 @@
 # GNU General Public License v3.0+ (see LICENSES/GPL-3.0-or-later.txt or https://www.gnu.org/licenses/gpl-3.0.txt)
 # SPDX-License-Identifier: GPL-3.0-or-later
 
-SASS=${SASS_COMPILER:-$(which sass)}
-POSTCSS=${POSTCSS:-$(which postcss)}
+SASS=${SASS_COMPILER:-node_modules/.bin/sass}
+POSTCSS=${POSTCSS:-node_modules/.bin/postcss}
 
-if [ "${SASS}" == "" ]; then
-    echo "Need 'sass' on path. You can install sass with 'npm install sass'."
+if [ ! -x "${SASS}" ]; then
+    echo "${SASS} is not executable. Did you run 'npm install'?"
     exit -1
 fi
 
-if [ "${POSTCSS}" == "" ]; then
-    echo "Need 'postcss' on path. You can install postcss and the required plugins with 'npm install autoprefixer cssnano postcss postcss-cli'."
+if [ ! -x "${POSTCSS}" ]; then
+    echo "${POSTCSS} is not executable. Did you run 'npm install'?"
     exit -1
 fi