Nostalgic style (5)
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">nostalgic style</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for retro that I've seen before include "Imitating a style from the recent past" , "sort of rocket" , "Reminiscent of a past style" , "Looking back" , "In a backward-looking style" .)