一种可能的解决方案是将动态特性用作选择器：

import sys

from PySide2.QtWidgets import QApplication, QLineEdit

class LineEdit(QLineEdit):
    QSS = """
    QLineEdit {
        font: 10pt "MS Shell Dlg 2";
        border-radius: 10px;
        border: 2px solid rgb(55,55,55);
        color: rgb(255, 255, 255);
        padding-left: 20px;
        padding-right: 20px;
        background-color: rgb(70,70,70);
    }
    QLineEdit:hover {
        border: 2px solid rgb(85,85,85);
    }
    QLineEdit:focus{
        border: 2px solid rgb(85, 170, 255);
    }
    QLineEdit[invalid="true"]{
        border: 2px solid rgb(255, 115, 107);
    }"""

    def __init__(self, parent=None):
        super().__init__(parent)
        self.textChanged.connect(self._handle_textChanged)
        self.setProperty("invalid", False)
        self.setStyleSheet(self.QSS)
        self._handle_textChanged()

    def _handle_textChanged(self):
        self.setProperty("invalid", not self.isValid())
        self.style().polish(self)

    def isValid(self):
        return len(self.text()) % 2 == 0

def main():
    app = QApplication(sys.argv)
    w = LineEdit()
    w.show()
    sys.exit(app.exec_())

if __name__ == "__main__":
    main()