You want to make the label of the form appear inside the input field.
Use the below code in a custom html block on a landing page with a form:
- remove the current labels in the form editor
- place the complete code (attached) in a custom html block on the page with the form
- View the live page to the see the changes
This code uses the field "id" you could use "name" instead.
This does not work for "select" fields