Function that generates a stylesheet for styling the QTabWidget, supporting four tab positions.

style_QTabWidget.py

import sys
from qtpy.QtWidgets import (
    QApplication,
    QMainWindow,
    QTabWidget,
    QFrame,
    QVBoxLayout,
)


def style_QTabWidget(
    border_color: str = "#b0b0b0",
    pane_bg_color: str = "#e0e0e0",
    tab_bg_color: str = "#d0d0d0",
    tab_fg_color: str = "#707070",
    active_fg_color: str = "#404040",
    border_width: str = "1px",
    tab_radius: str = "4px",
    tab_vertical_padding: str = "2px",
    tab_horizontal_padding: str = "4px",
):
    """
    `border_color`: color of the border of the tab widget.
    `pane_bg_color`: color of the background of the tabpane & the selected tab.
    `tab_bg_color`: color of the background of the unselected tab.
    `tab_fg_color`: color of the text of the unselected tab.
    `active_fg_color`: color of the text of the selected tab.
    `border_width`: width of the border of the tab widget.
    `tab_radius`: radius of the border of the tabs.
    `tab_vertical_padding`: vertical padding of the North & South tabs,
        or horizontal padding of the West & East tabs.
    `tab_horizontal_padding`: horizontal padding of the North & South tabs,
        or vertical padding of the West & East tabs.
    """

    qss = f"""
        QTabWidget::pane {{
            border: {border_width} solid {border_color};
            background-color: {pane_bg_color};
        }}
        QTabBar::tab {{
            border-radius: {tab_radius};
            border: {border_width} solid {border_color};
            background-color: {tab_bg_color};
            color: {tab_fg_color};
            
        }}
        QTabBar::tab:selected {{
            background-color: {pane_bg_color};
            color: {active_fg_color};
        }}
        QTabWidget[tabPosition="North"] > QTabBar::tab, QTabWidget[tabPosition="South"] > QTabBar::tab {{
            padding: {tab_vertical_padding} {tab_horizontal_padding};
        }}
        QTabWidget[tabPosition="West"] > QTabBar::tab, QTabWidget[tabPosition="East"] > QTabBar::tab {{
            padding: {tab_horizontal_padding} {tab_vertical_padding};
        }}
        QTabWidget[tabPosition="North"]:tab-bar {{
            top: {border_width};
        }}
        QTabWidget[tabPosition="North"] > QTabBar::tab {{
            border-bottom-left-radius: 0px;
            border-bottom-right-radius: 0px;
        }}
        QTabWidget[tabPosition="North"] > QTabBar::tab:selected {{
            border-bottom: none;
        }}
        QTabWidget[tabPosition="South"]:tab-bar {{
            bottom: {border_width};
        }}
        QTabWidget[tabPosition="South"] > QTabBar::tab {{
            border-top-left-radius: 0px;
            border-top-right-radius: 0px;
        }}
        QTabWidget[tabPosition="South"] > QTabBar::tab:selected {{
            border-top: none;
        }}
        QTabWidget[tabPosition="West"]:tab-bar {{
            left: {border_width};
        }}
        QTabWidget[tabPosition="West"] > QTabBar::tab {{
            border-top-right-radius: 0px;
            border-bottom-right-radius: 0px;
        }}
        QTabWidget[tabPosition="West"] > QTabBar::tab:selected {{
            border-right: none;
        }}
        QTabWidget[tabPosition="East"]:tab-bar {{
            right: {border_width};
        }}
        QTabWidget[tabPosition="East"] > QTabBar::tab {{
            border-top-left-radius: 0px;
            border-bottom-left-radius: 0px;
        }}
        QTabWidget[tabPosition="East"] > QTabBar::tab:selected {{
            border-left: none;
        }}
        """

    return qss


class Frame(QFrame):
    def __init__(self, parent=None):
        super().__init__(parent)
        layout = QVBoxLayout()
        self.tabs = {}
        for e in QTabWidget.TabPosition:
            w = QTabWidget()
            w.setTabPosition(e)
            for i in range(3):
                w.addTab(QFrame(w), f"{e.name} {i}")
            layout.addWidget(w)
            self.tabs[e] = w
        self.setLayout(layout)


def main():
    app = QApplication(sys.argv)
    app.setStyleSheet(style_QTabWidget())
    w = QMainWindow()
    w.setMinimumSize(800, 600)
    w.setCentralWidget(Frame(w))
    w.show()
    sys.exit(app.exec())