To make text accessible and resize the solution is to use relative fonts:
body { font-size:medium; }
When text is resized through a browser all font sizes should change relatively. Unfortunately this does not apply to the <input> and <textarea> tags and so the text size does not change.
Fear not though, the simple solution is to simply set a percentage value to the input and textarea selectors:
input, textarea { font-size:100%; }
Now the text in the <input> and <textarea> tags should resize correctly.