fixed preview

static/style.css

 .videopreview > li:nth-child(even) { background: #f5f5f5; }
 .courses-list li:nth-child(even) { background: #fAfAfA; }
-.list-group-item-condensed { padding: 2px !important; }
+
+@media (min-width: 767px) {
+	.list-group-item-condensed { padding-top: 2px !important; padding-bottom: 2px !important; }
+}

templates/macros.html

@@ -19,7 +19,7 @@
 	<a class="visible-xs" href="{{url_for('lecture', id=lecture['id'])}}" title="{{ lecture['coursetitle'] }}" style="color: #000">
 		<ul class="list-unstyled">
 			<li>
-				<img src="{{ config.VIDEOPREFIX }}/{{ lecture['titlefile'] }}" alt="Vorschaubild">
+				<img style="width: 100%;" src="{{ config.VIDEOPREFIX }}/{{ lecture['titlefile'] }}" alt="Vorschaubild">
 			</li>
 			<li>
 				<strong>{{ lecture['short'] }}</strong>	{{ lecture['time'] }}