Add postcss to the frontend setup

Author: bikkelhart-menno

.gitignore

@@ -79,3 +79,7 @@ docker/local.env
 
 # config dumps from make docker-compose-config-to-file
 config-compose-*
+
+# Frontend
+frontend/node_modules
+frontend/build

frontend/.stylelintrc.json

@@ -0,0 +1 @@
+{ "extends": ["stylelint-config-standard"] }

frontend/css/style-test.css

@@ -0,0 +1,25 @@
+/* Test file for postcss output */
+:root {
+  color-scheme: light dark;
+}
+
+body {
+  color: light-dark(#333b3c, #efefec);
+  background-color: light-dark(#efedea, #223a2c);
+}
+
+input {
+  /* styles for input not in a label  */
+  border: tomato 2px solid;
+}
+
+label {
+  /* styles for label */
+  font-family: system-ui;
+  font-size: 1.25rem;
+
+  & input {
+    /* styles for input in a label  */
+    border: blue 2px dashed;
+  }
+}