Global stylesheet isn't fully working - qt

Question

I'm trying to set a global stylesheet for all my buttons.
Doing it for a specific button like the following, works as expected:
button->setStyleSheet(QString("QPushButton:focus {") +
"outline: 0;" +
"background-color: #" + BUTTON_HIGHLIGHT_BG_COLOR + "; " +
"color: #" + BUTTON_HIGHLIGHT_TXT_COLOR + "; " +
"}"
);
But if I make it global, like this:
qApp->setStyleSheet(QString("QPushButton:focus {") +
"outline: 0;" +
"background-color: #" + BUTTON_HIGHLIGHT_BG_COLOR + "; " +
"color: #" + BUTTON_HIGHLIGHT_TXT_COLOR + "; " +
"}"
);
the focused buttons get the correct font color, but they don't seem to have a background (although the background I'm setting for them is different from the main layout's background.)
BUTTON_HIGHLIGHT_BG_COLOR and BUTTON_HIGHLIGHT_TXT_COLOR are strings for colors (e.g. "FF0000")
What could be the cause that it works for a specific widget, but fails globally?
update:
I followed #ThorngardSO's answer and finally solved it by changing:
stackedWidget->setStyleSheet("background-color: white;");
to:
stackedWidget->setStyleSheet("QStackedWidget { background-color: white; }");
which was in the loading screen (first screen)

Answer 1

You should try to narrow it down as much as possible:
Is this the only rule in your global stylesheet? If not, remove all other rules for testing purposes and see what happens.
Get a clear grasp on the widget-hierachy of your button (perhaps it's the child of a groupbox which is itself a child of a mainwindow), and then check:
Do any of those widgets in the hierachy have a stylesheet set? If yes, remove those stylesheets for testing purposes and see what happens.
Do you, at any time, call functions like setPalette() or setAutoFillBackground() on any of the widgets in the hierachy (or have the auto-fill-background property set in the designer)? If yes, remove those calls and see what happens.

Answer 2

Not that it's your problem, but you're assembling that constant string at runtime from bits and pieces. Don't do that. Instead, you can simply concatenate string literals in C and C++ simply by putting them next to each other.
qApp->setStyleSheet(QStringLiteral(
"QPushButton:focus {"
"outline: 0;"
"background-color: #" BUTTON_HIGHLIGHT_BG_COLOR "; "
"color: #" BUTTON_HIGHLIGHT_TXT_COLOR "; "
"}"
));
If you wanted the colors to be changeable at runtime, use the %-substitution:
qApp->setStyleSheet(QStringLiteral(
"QPushButton:focus {"
"outline: 0;"
"background-color: #%1; "
"color: #%2; "
"}"
).arg(background).arg(foreground));