fix(legacy): style insert order (#13266)

Co-authored-by: sapphi-red <green@sapphi.red>

Author: lsdsjy

packages/vite/src/node/plugins/css.ts

@@ -636,10 +636,10 @@ export function cssPostPlugin(config: ResolvedConfig): Plugin {
  `${style}.textContent = ${cssString};` +
  `document.head.appendChild(${style});`
  const wrapIdx = code.indexOf('System.register')
- const insertMark = "'use strict';"
- const insertIdx = code.indexOf(insertMark, wrapIdx)
+ const executeFnStart =
+  code.indexOf('{', code.indexOf('execute:', wrapIdx)) + 1
  const s = new MagicString(code)
- s.appendLeft(insertIdx + insertMark.length, injectCode)
+ s.appendRight(executeFnStart, injectCode)
  if (config.build.sourcemap) {
  // resolve public URL from CSS paths, we need to use absolute paths
  return {