fix(ui): center dialogs again after the global margin reset

tests/test_ui_dialogs.py

@@ -97,6 +97,8 @@ def test_import_dialog_opens_and_closes(page):
     page.click("[data-quick='0']")
     page.wait_for_selector("#quick-dialog[open]")
     assert page.locator("#quick-dialog").is_visible()
+    box = page.locator("#quick-dialog").bounding_box()
+    assert abs(box["x"] + box["width"] / 2 - 600) < 10  # centered in the viewport
     # everything reachable, nothing cut off at the bottom
     for sel in ("#quick-m-submit", "#quick-close"):
         box = page.locator(sel).bounding_box()