How to Change `collection_check_boxes` into X Boxes (aka ticks into crosses)?

Question

With this...

  <%= f.label "Level 1:" %>&nbsp;
  <%= f.collection_check_boxes :missed, Habit::ONEMISSED, :downcase, :to_s %>

I get this (assuming the user clicked on the first checkbox):

[ √ ]"X"  [  ]"X"  [  ]"X"

What would I need instead so that when the user clicks on a checkbox it shows an X instead of a checkmark?

For example:

[ X ]  [  ]  [  ]

The latter case looks cleaner.