import sys
import PySide6

from PySide6 import QtGui, QtWidgets
from PySide6.QtCore import Qt
from PySide6.QtGui import QPixmap
from PySide6.QtWidgets import *

app = QApplication(sys.argv)

win = QWidget()
win.setWindowTitle("Belka tytułowa")
win.setGeometry(100,100,580,400)
win.move(int(1920/2), int(1080/2))
win.setStyleSheet("background-color: white;")

lay = QHBoxLayout()

#BUTTONS

btn1 = QPushButton(win)
btn1.setText("Btn1")

btn2 = QPushButton(win)
btn2.setText("Btn2")

btn3 = QPushButton(win)
btn3.setText("Btn3")

btn4 = QPushButton(win)
btn4.setText("Btn4")

lay.addWidget(btn1)
lay.addWidget(btn2)
lay.addWidget(btn3)
lay.addWidget(btn4)

if win.width() < 400:
    win.setStyleSheet("background-color: red;")
else:
    win.setStyleSheet("background-color: white;")
    

win.setLayout(lay)

win.show()