Override float: left for radio buttons from khan-exercises

Summary:
Fixes a bug with displaying radios in the answer area. Most visible in
firefox, but shows up in chrome too

Test Plan:
open
http://localhost:9000/test.html#content={%22question%22%3A{%22content%22%3A%22[[%E2%98%83%20radio%201]]%22%2C%22widgets%22%3A{%22radio%201%22%3A{%22type%22%3A%22radio%22%2C%22graded%22%3Atrue%2C%22options%22%3A{%22choices%22%3A[{%22content%22%3A%22Hi%22}]%2C%22randomize%22%3Afalse%2C%22multipleSelect%22%3Afalse}}}}%2C%22answerArea%22%3A{%22type%22%3A%22multiple%22%2C%22options%22%3A{%22content%22%3A%22[[%E2%98%83%20radio%201]]%22%2C%22widgets%22%3A{%22radio%201%22%3A{%22type%22%3A%22radio%22%2C%22graded%22%3Atrue%2C%22options%22%3A{%22choices%22%3A[{%22content%22%3A%22bye%22}%2C{%22content%22%3A%22why%22}]%2C%22randomize%22%3Afalse%2C%22multipleSelect%22%3Afalse}}}}%2C%22calculator%22%3Afalse}%2C%22hints%22%3A[{%22content%22%3A%22Here%27s%20one%20way%20to%20make%20an%20angle%20with%20these%20points%2C%20but%20this%20angle%20is%20acute%2C%20not%20obtuse!%20%20\n![]%28https%3A%2F%2Fka-perseus-images.s3.amazonaws.com%2F93fd1b71b55ca18f4a81ad0520df8c96e07125f4.png%29%22%2C%22widgets%22%3A{}}%2C{%22content%22%3A%22Here%20is%20the%20way%20to%20make%20an%20obtuse%20angle%20in%20this%20situation.%20It%27s%20an%20obtuse%20angle%20because%20its%20measure%20is%20greater%20than%20%2490%24%20degrees.%20%20\n![]%28https%3A%2F%2Fka-perseus-images.s3.amazonaws.com%2F303cfd47cb758adc31af8f80d440827199c6bc63.png%29%22%2C%22widgets%22%3A{}}]}
in firefox
 * is the answer checkbox not underneath text? yay

Auditors: alpert