Selection does not stay inside window when inside split container

[LunaMeadows]

Describe the bug

When adding a selection in a split container, the selection does not set the width properly and goes outside of the container.

import toga
from toga.style.pack import COLUMN, Pack, BOTTOM, ROW, CENTER, JUSTIFY, RIGHT
def build(app):
    right_container = toga.Box(id='OptionsPane', style=Pack(direction=COLUMN, alignment=RIGHT))
    camera_options_box = toga.Box(id='camButtons', style=Pack(direction=ROW, alignment=CENTER))
    button_previous_cam = toga.Button('Previous', style=Pack(width=100, padding=20, padding_top=0))
    label_cam = toga.Label('next', style=Pack(width=100, padding=20, padding_top=10, text_align=CENTER))
    button_next_cam = toga.Button('next', style=Pack(width=100, padding=20, padding_top=0))
    camera_options_box.add(button_previous_cam, label_cam, button_next_cam)
    image_camera_viewer = toga.ImageView(image=toga.Image('0_0.jpg'), style=Pack(width=420, height=420))
    selection_image_dropdown = toga.Selection(items=['Test'])

    right_container.add(camera_options_box, image_camera_viewer, selection_image_dropdown)

    box2 = toga.Box(style=Pack(direction=COLUMN, alignment=CENTER))

    box2.add(
        toga.Selection('Preset Selection', items=[''], style=Pack(width=200)),
        toga.Button('Load Preset', style=Pack(width=200)),
        toga.Button('Edit Preset', style=Pack(width=200)),
        toga.Button('Delete Preset', style=Pack(width=200)),
        toga.Button('New Preset', style=Pack(width=200)),
        toga.Box(style=Pack(direction=COLUMN, flex=1)),
        toga.Button('Map Cameras', style=Pack(width=200)),
    )

    split = toga.SplitContainer()
    split.content = [(box2, .3), (right_container, .7)]

    return split

    return box


def main():
    return toga.App("Testing", "org.test.test", startup=build)


if __name__ == "__main__":
    main().main_loop()

Steps to reproduce

Add selection to splitcontainer

Expected behavior

Selection should stay within the split container

Screenshots

No response

Environment

• Operating System: Ubuntu 20.04
• Python version: 3.8
• Software versions:
  • Briefcase:
  • Toga: 0.3.0
  • ...

Logs

Additional context

No response

[mhsmith]

Can you add some screenshots showing the problem?

[LunaMeadows]

Apologizes, I thought I did. As you can see the end of the selection box is going outside of the screen.

[mhsmith]

Thanks: I've tested your example and confirmed that this issue will be fixed by #1794.