UI: Use the QAbstractButton API to set the icon and icon size for the TitleBar

src/UI/TitleBar.cc

@@ -27,12 +27,12 @@ TitleBar::TitleBar(const QIcon &icon, const QString &title, QWidget *parent) noe
     iconLabel->setPixmap(icon.pixmap(icon.actualSize(QSize(32, 32))));
     titleLabel->setTextInteractionFlags(Qt::NoTextInteraction);
     titleLabel->setSizePolicy(QSizePolicy::MinimumExpanding, QSizePolicy::Fixed);
+    closeButton->setIconSize(QSize(22, 22));
+    closeButton->setIcon(QIcon(VIVY_ICON_CLOSE));
     closeButton->setFlat(true);
     closeButton->setDefault(false);
     closeButton->setStyleSheet("color:  #1394B4;"
-                               "border:         none;"
-                               "icon:           url(" VIVY_ICON_CLOSE ");"
-                               "icon-size:      22px;");
+                               "border: none;");
 
     titleLayout->addWidget(iconLabel);
     titleLayout->addWidget(titleLabel);