fix: don't lowercase custom selectors variable name #4254 (#4255)

* fix: don't lowercase custom selectors variable name #4254

* proper fix for camelCased custom selector

* Move customs-selectors case snapshots to correct place

src/language-css/printer-postcss.js

@@ -959,6 +959,7 @@ function maybeToLowerCase(value) {
     value.includes("#") ||
     value.startsWith("%") ||
     value.startsWith("--") ||
+    value.startsWith(":--") ||
     (value.includes("(") && value.includes(")"))
     ? value
     : value.toLowerCase();

tests/css_case/__snapshots__/jsfmt.spec.js.snap

@@ -748,3 +748,18 @@ table {
 }
 
 `;
+
+exports[`custom-selectors.css 1`] = `
+@custom-selector :--camelCase .my-css-selector;
+
+:--camelCase {
+  content: red;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+@custom-selector :--camelCase .my-css-selector;
+
+:--camelCase {
+  content: red;
+}
+
+`;

tests/css_case/custom-selectors.css

@@ -0,0 +1,5 @@
+@custom-selector :--camelCase .my-css-selector;
+
+:--camelCase {
+  content: red;
+}