style: add space above volume control

Co-authored-by: Tom Ernst <tom@citr.one>

app/static/style.css

@@ -106,6 +106,7 @@ button:hover, button:focus {
 }
 
 .controls button { flex: 1; }
+.controls + label { margin-top: 4px; }
 .controls .stacked-play {
   display: flex;
   flex-direction: column;