How do I tweak the CSS of the registration form?

The easiest way to tweak the CSS is by any 3rd-party plugin that enables you to add CSS code like "My Custom CSS" or "JetPack" CSS option. Both options load the CSS after the regular CSS files and enable you to change anything that you want. The widget uses many classes and IDs that enable you to change an part of the overall design using CSS. You can use any online websites to learn CSS, Firebug on FireFox or "Inspect Element" on Chrome to find the correct CSS class for your needs. Just an important note, incorrect CSS design can cause the plugin not to work as our real-time validation setting that uses jQuery needs specific IDs to be visible in order to work, so you need to be careful when changing the CSS of the registration form.