<div class="legend" style="direction:ltr;line-height:23px;"><div class="legend-content" style="display:inline-block;vertical-align:top;box-sizing:border-box;width:34px;height:23px;overflow:hidden;font-size:15px;border:thin solid #333;background:darkblue;color:#202122;text-align:center;"> </div> Founders ('50s)</div><div class="legend" style="direction:ltr;line-height:23px;"><div class="legend-content" style="display:inline-block;vertical-align:top;box-sizing:border-box;width:34px;height:23px;overflow:hidden;font-size:15px;border:thin solid #333;background:blue;color:#202122;text-align:center;"> </div> First enlargement ('73)</div><div class="legend" style="direction:ltr;line-height:23px;"><div class="legend-content" style="display:inline-block;vertical-align:top;box-sizing:border-box;width:34px;height:23px;overflow:hidden;font-size:15px;border:thin solid #333;background:turquoise;color:#202122;text-align:center;"> </div> Mediterranean enlargement ('80s)</div><div class="legend" style="direction:ltr;line-height:23px;"><div class="legend-content" style="display:inline-block;vertical-align:top;box-sizing:border-box;width:34px;height:23px;overflow:hidden;font-size:15px;border:thin solid #333;background:green;color:#202122;text-align:center;"> </div> EFTA &amp; East Germany ('90s)</div><div class="legend" style="direction:ltr;line-height:23px;"><div class="legend-content" style="display:inline-block;vertical-align:top;box-sizing:border-box;width:34px;height:23px;overflow:hidden;font-size:15px;border:thin solid #333;background:yellow;color:#202122;text-align:center;"> </div> Eastern bloc enlargements ('00s)</div><div class="legend" style="direction:ltr;line-height:23px;"><div class="legend-content" style="display:inline-block;vertical-align:top;box-sizing:border-box;width:34px;height:23px;overflow:hidden;font-size:15px;border:thin solid #333;background:red;color:#202122;text-align:center;"> </div> Referendum failed</div>
<a href="//commons.wikimedia.org/wiki/User:JLogan" title="User:JLogan">JLogan</a>
CC BY-SA 3.0
Own work adapted from base map <a href="//commons.wikimedia.org/wiki/File:European_Union.png" title="File:European Union.png">Image:European Union.png</a> (free image on Commons)