style(ui): enlarge volume +/- buttons (18->30px) and volume %% (11->14px)

web/static/style.css

@@ -219,6 +219,7 @@ html, body {
 #volume-row > * + * { margin-left: 10px; }
 .btn-vol { width: 48px; height: 48px; line-height: 48px; -webkit-flex-shrink: 0; flex-shrink: 0; font-size: 18px; }
 #btn-mute { font-size: 22px; }
+#btn-vol-up, #btn-vol-down { font-size: 30px; font-weight: 600; }
 #btn-mute.muted { color: var(--accent); }
 #volume-bar-wrap {
   -webkit-flex: 1;
@@ -245,7 +246,7 @@ html, body {
   border-radius: 4px;
 }
 #volume-pct {
-  font-size: 11px;
+  font-size: 14px;
   color: var(--text-dim);
   text-align: center;
 }