I would like to modify the way that the list of the different options of my datalist are displayed. Is it possible to apply on it some CSS properties ?
<input list="languages" id="language_id" />
<option value="ruby-on-rails">Ruby on Rails</option>
Like select elements, the datalist element has very little flexibility in styling. You cannot style any of the suggested terms if that's what your question was asking.
Browsers define their own styles for these elements.