fix: use One Dark theme for CodeMirror syntax highlighting

- Replace custom highlight styles with @codemirror/theme-one-dark
- Cleaner implementation with official CodeMirror theme
- Keep custom font and padding overrides

package.json

@@ -38,6 +38,7 @@
 		"@codemirror/lang-css": "^6.3.1",
 		"@codemirror/lang-html": "^6.4.11",
 		"@codemirror/state": "^6.5.2",
+		"@codemirror/theme-one-dark": "^6.1.3",
 		"@codemirror/view": "^6.39.4",
 		"@emmetio/codemirror6-plugin": "^0.4.0",
 		"codemirror": "^6.0.2",