Simplify css-prefix scripts. (#29205)

package.json

@@ -39,7 +39,7 @@
     "css-minify-docs": "cross-env-shell cleancss --level 1 --format breakWith=lf --source-map --source-map-inline-sources --output site/docs/$npm_package_version_short/assets/css/docs.min.css site/docs/$npm_package_version_short/assets/css/docs.min.css",
     "css-prefix": "npm-run-all --parallel css-prefix-*",
     "css-prefix-main": "postcss --config build/postcss.config.js --replace \"dist/css/*.css\" \"!dist/css/*.min.css\"",
-    "css-prefix-docs": "postcss --config build/postcss.config.js --replace \"site/docs/**/*.css\" \"site/docs/**/*.css\"",
+    "css-prefix-docs": "postcss --config build/postcss.config.js --replace \"site/docs/**/*.css\"",
     "js": "npm-run-all js-compile js-minify js-copy",
     "js-copy": "cross-env-shell shx mkdir -p site/docs/$npm_package_version_short/dist/ && cross-env-shell shx cp -r dist/js/ site/docs/$npm_package_version_short/dist/",
     "js-main": "npm-run-all js-lint js-compile js-minify-main",