I’m afraid checkboxes/radio buttons are elements generated by the browser not by Gravity Forms so they can’t be customized easily only with CSS as you can do with other elements of the form.
Regarding to the choices label vertical alignment, please check the following CSS targeting examples:
Please check the following doc page for instructions about where to add your custom CSS: https://docs.gravityforms.com/where-to-put-your-custom-css/
Also if you’re using any caching solution make sure that your have flushed the cache and turned it off while you’re working in the CSS changes. And empty your browser cache too to see the changes.