#include <QtWidgets>

class LineEdit : public QLineEdit
{
public:
  using QLineEdit::QLineEdit;
  QGraphicsDropShadowEffect* dse = nullptr;

  void focusInEvent(QFocusEvent* event)
  {
    dse = new QGraphicsDropShadowEffect();
    dse->setBlurRadius(60);
    dse->setOffset(0);
    dse->setColor(0x007eff);
    setGraphicsEffect(dse);
    QLineEdit::focusInEvent(event);
  }

  void focusOutEvent(QFocusEvent* event)
  {
    dse->deleteLater();
    QLineEdit::focusOutEvent(event);
  }
};

int main(int argc, char **argv)
{
  QApplication app(argc, argv);
  QWidget w;
  QHBoxLayout hLay(&w);
  hLay.setSpacing(10);
  QLineEdit le1;
  LineEdit le2;
  hLay.addWidget(&le1);
  hLay.addWidget(&le2);
  w.show();
  return app.exec();
}