theme：添加flatgray主题。

MainWidget.cpp

@@ -1,6 +1,7 @@
 #include "MainWidget.h"
 #include <QClipboard>
 #include <QSettings>
+#include <QFile>
 #include "./ui_MainWidget.h"
 
 constexpr std::size_t g_OnePage = 100;
@@ -55,6 +56,11 @@ MainWidget::MainWidget(QWidget* parent) : QWidget(parent), ui(new Ui::MainWidget
     settings.beginGroup("xmlopr");
     restoreGeometry(settings.value("geometry").toByteArray());
     settings.endGroup();
+
+    QFile qss_file("://qss/flatgray.css");
+    if (qss_file.open(QFile::ReadOnly)) {
+        qApp->setStyleSheet(qss_file.readAll());
+    }
 }
 
 void MainWidget::copy_key()