How to add a nested layers and widgets?

I'm having trouble with the layout of the following program. I want to insert a QHBoxLayout into the first row (or any row for that matter) of a QVBoxLayout. Goal is to achieve something like this:

Here is what I have so far:

import sys, os
from PyQt5.QtWidgets import *
from PyQt5.QtWebEngineWidgets import QWebEngineView
from PyQt5.QtGui import *
from PyQt5.QtCore import *

class MainWindow(QMainWindow):

    def __init__(self, *args, **kwargs):
        super(MainWindow, self).__init__(*args, **kwargs)

        self.setFixedSize(600, 600)

        layout = QVBoxLayout()
        layout.setContentsMargins(0,0,0,0)
        layout.setAlignment(Qt.AlignLeft | Qt.AlignTop)

        self.webEngineView = QWebEngineView()
        self.loadPage()
        self.webEngineView.setFixedSize(QSize(600, 280))
        layout.addWidget(self.webEngineView)

        button = QPushButton("CLICK", self) 
        button.setFixedSize(QSize(50, 80))
        button.clicked.connect(self.clickme)
        button.setStyleSheet("""
        background-color: red;
        """)
        layout.addWidget(button)

        # without this part the code works fine:
        titlelayout = QHBoxLayout()
        titlelayout.setContentsMargins(0,0,0,0)
        titlelayout.setAlignment(Qt.AlignRight | Qt.AlignTop)
        button1 = QPushButton("CLICK", self) 
        button1.setFixedSize(QSize(40, 40))
        titlelayout.addWidget(button1)
        titlelayout.addLayout(layout)

        widget = QWidget()
        widget.setLayout(layout)
        self.setCentralWidget(widget)

    def loadPage(self):

        html = '''
        <html style="width: 100%; height: 100%; margin: 0; padding: 0;">
        <body style="overflow: hidden; width: 100%; height: 100%; margin: 0; padding: 0; background-color: #E6E6FA;">
        
        </body>
        </html>'''

        self.webEngineView.setHtml(html)

    def clickme(self): 
        print("clicked")

app = QApplication(sys.argv)
app.setStyleSheet("QMainWindow {background-color:white}")
window = MainWindow()
window.show()
sys.exit(app.exec_())

Solution

In my designs I prefer not to place a layout inside another layout but to use a QWidget as a container to be the intermediary:

import sys

from PyQt5.QtCore import QSize, Qt
from PyQt5.QtWidgets import (
    QApplication,
    QGridLayout,
    QHBoxLayout,
    QLineEdit,
    QMainWindow,
    QPushButton,
    QVBoxLayout,
    QWidget,
)
from PyQt5.QtWebEngineWidgets import QWebEngineView


class MainWindow(QMainWindow):
    def __init__(self, *args, **kwargs):
        super(MainWindow, self).__init__(*args, **kwargs)

        self.setFixedSize(600, 600)

        self.webEngineView = QWebEngineView()

        button1 = QPushButton("CLICK")
        button1.setFixedSize(QSize(50, 80))
        button1.setStyleSheet("""background-color: red;""")
        button1.clicked.connect(self.clickme)

        button2 = QPushButton("CLICK")
        button2.setFixedSize(QSize(50, 80))

        button3 = QPushButton("CLICK")
        button3.setFixedSize(QSize(50, 80))

        title_widget = QWidget()
        hlay = QHBoxLayout(title_widget)
        hlay.addWidget(button1, alignment=Qt.AlignLeft)
        hlay.addStretch()
        hlay.addWidget(button2, alignment=Qt.AlignRight)
        hlay.addWidget(button3, alignment=Qt.AlignRight)

        footer_widget = QWidget()

        hlay2 = QGridLayout(footer_widget)
        hlay2.addWidget(QPushButton("Foo"), 0, 0)
        hlay2.addWidget(QLineEdit("Bar"), 1, 0, 1, 2)

        central_widget = QWidget()
        self.setCentralWidget(central_widget)

        vlayout = QVBoxLayout(central_widget)
        vlayout.addWidget(title_widget)
        vlayout.addWidget(self.webEngineView, stretch=1)
        vlayout.addWidget(footer_widget)

        self.loadPage()

    def loadPage(self):

        html = """
        <html style="width: 100%; height: 100%; margin: 0; padding: 0;">
        <body style="overflow: hidden; width: 100%; height: 100%; margin: 0; padding: 0; background-color: #E6E6FA;">
        
        </body>
        </html>"""

        self.webEngineView.setHtml(html)

    def clickme(self):
        print("clicked")


app = QApplication(sys.argv)
app.setStyleSheet("QMainWindow {background-color:white}")
window = MainWindow()
window.show()
sys.exit(app.exec_())