Does anyone know how to center text-entry boxes?

Assuming you are using a Text entry style question, add the following to the html of the question:

<style>
.ChoiceStructure {
text-align: center;
}
</style>

If you have multiple questions on the page and you only want to center this one, try adding the following Javascript to the Question:

Qualtrics.SurveyEngine.addOnReady(function()
{
this.questionContainer.select('.ChoiceStructure')[0].style = 'text-align: center;';
});