PySide2应用中使用CSS自定义属性（变量）时样式解析失败

核心错误点 #

1. Qt样式表(QSS)不支持CSS变量和:root选择器：你用的--dark这类自定义属性和:root是标准CSS特性，但QSS并不兼容，这是样式表解析失败的主要原因。
2. border-radius语法错误：QSS中多个圆角值需要用空格分隔，而非逗号。
3. 占位符选择器不兼容：标准CSS的::placeholder在QSS中无效，需改用QLineEdit::placeholder-text。
4. QMainWindow布局问题：QMainWindow默认没有顶层布局，直接调用self.layout()会返回None，无法添加部件。
5. 样式未刷新：设置部件的自定义property后，需要手动触发样式刷新才能生效。

修正后的代码 #

import sys, re

from module.widgets   import RuWidgets
from module.functions import *
from module.statics   import *

from PySide2.QtGui     import QFont, QFontDatabase, QIcon, QCursor
from PySide2.QtCore    import Qt, Signal, QThread, QPoint, QSettings
from PySide2.QtWidgets import QApplication, QMainWindow, QFrame, QMenu, QLineEdit, QWidget, QVBoxLayout

class Patrick(QMainWindow):
    custom_colors = None

    def __init__(self):
        super().__init__()
        
        data = readJSON(CONFIGURATION, 'data')

        self.setWindowFlag(Qt.FramelessWindowHint)
        self.setAttribute(Qt.WA_TranslucentBackground)
        self.setWindowTitle(NAME)
        self.setFixedSize(WIDTH, HEIGHT)
        
        # 替换CSS变量为直接写值，修正QSS语法
        self.setStyleSheet(
            """
            #normal {
                background-color: #483939;
                color: #D9D9D9;
            }

            #inverted {
                background-color: #D9D9D9;
                color: #483939;
            }

            .full_rounded {
                border-radius: 8px 8px 8px 8px;
            }

            .top_rounded {
                border-radius: 0px 0px 8px 8px;
            }

            QLineEdit::placeholder-text {
                color: #9C8181;
            }
            """
        )

        # 给QMainWindow设置中心部件和布局
        central_widget = QWidget()
        self.setCentralWidget(central_widget)
        layout = QVBoxLayout(central_widget)
        layout.setContentsMargins(0, 0, 0, 0)  # 去掉默认边距

        background = QFrame()
        background.setFixedSize(WIDTH, HEIGHT)
        bar = QFrame()
        bar.setFixedSize(WIDTH, WIDGET_HEIGHT)

        for widget, object_name, object_class in [
            (background, 'normal', 'full_rounded'),
            (bar, 'inverted', 'top_rounded')
        ]:
            widget.setObjectName(object_name)
            widget.setProperty(object_class, True)
            # 设置property后刷新样式
            widget.style().unpolish(widget)
            widget.style().polish(widget)

        for widget in [
            background,
            bar
        ]:
            layout.addWidget(widget)

        self.show()

if __name__ == '__main__':
    application = QApplication(sys.argv)

    window = Patrick()
    
    #font = QFont(
    #    QFontDatabase.applicationFontFamilies(
    #        QFontDatabase.addApplicationFont(
    #            FONT.format('Inter-Regular')
    #        )
    #    )[0]
    #)
    #font.setPointSize(FONT_SIZE)  # 修正：pointSize()是获取值，设置用setPointSize()
    
    #application.setFont(font)
    application.exec_()

额外说明 #

如果想实现类似CSS变量的复用效果，可以用Python变量拼接样式表，避免重复写颜色值：

dark_color = "#483939"
middle_color = "#9C8181"
light_color = "#D9D9D9"

style_sheet = f"""
#normal {{
    background-color: {dark_color};
    color: {light_color};
}}

#inverted {{
    background-color: {light_color};
    color: {dark_color};
}}

QLineEdit::placeholder-text {{
    color: {middle_color};
}}
"""
self.setStyleSheet(style_sheet)

内容的提问来源于stack exchange，提问作者Berdy Alexei Cadaeib Fecei