Wordpress validating forms
The sizing depends a bit on the context (mobile or not? It is likely these days that that someone is using your form on a touch device.
As an added benefit, if you specify a font size of 16 pixels for input sizes, i OS will not zoom in anymore when you tap a field, simply because it is not needed.
I love a nice looking form and a cool SVG animation as much as anyone, but you are actually doing your users a disservice by customising form elements without any added value.
What I mean by without added value is customising checkboxes and radio buttons purely for cosmetic reasons.
If the user typed Belgium as their country and they entered a phone number like 0495 20 12 12 you can assume it’s a cell phone number and store it as such.
All too often I spot a pretty radio button or checkbox that is broken in terms of interaction design.
However, customising the look of the fields often leads to confusing keyboard navigation.
90% of forms I test with customised checkboxes or radio buttons don’t have focus styles and are hard to navigate by keyboard.
When a form gets submitted, the user will end up on the same page, but you don’t know if the error is in the viewport.
Put both an error on top of the form (and make sure it is in the viewport on both desktop and mobile) as well as field specific explanations about what is wrong with the inputted data.