Unfortunately, this problem is caused by one of your plugins.
There are two ways to determine which one:
1) Using code inspector: go to the “styles” section and you’ll see which plugin CSS file influences
2) Deactivate your plugins one-by-one, meanwhile updating Captcha settings page. This way you’ll see which plugin creates the problem.
If you have programming skills, you can add the necessary CSS styles by yourself.
Please go to the plugin settings page, open “Custom code” tab, mark the “Activate” option in the “Editing bws-custom-code.css” section, and add the code you need.