The input fields are still ordinary input fields having the CSS property border-width set to 0,0,1,0.
You definitely won't break the specification, cause it's primarily for spacing, padding and typing behavior. The "official" specs for text input can be found at google. They give numerous examples including examples with full boxes, e.g. google maps search field.
Text fields allow the user to input text. They can be single-line, with or without scrolling, or multi-line, and can have an icon. Touching a text field places the cursor and automatically displays the keyboard. In addition to typing, text fields allow for a variety of other tasks, such as text selection (cut, copy, paste) and data lookup via auto-completion. See Patterns > Selection for text selection design.