[qt] fix closing software dialog color (#4305)

Signed-off-by: rayanmargham <rayanmargham4@gmail.com>

- [x] I have read and followed the [Contribution Guidelines](https://git.eden-emu.dev/eden-emu/eden/src/branch/master/CONTRIBUTING.md#code-contributions).
- [x] I have read and followed the [AI Policy](https://git.eden-emu.dev/eden-emu/eden/src/branch/master/docs/policies/AI.md)
- [x] I have read and followed the [Coding Guidelines](https://git.eden-emu.dev/eden-emu/eden/src/branch/master/docs/policies/Coding.md) to the best of my ability.

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This change fixes the closing software dialogue box having really grayish to white text on a white background making it impossible to read. This fixes default-dark giving it this look with the attached screenshot![image](/attachments/ad7dd13c-3808-4a0e-b29b-1a001a1106e0)

Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/4305
Reviewed-by: Lizzie and Samuel <lizzie@eden-emu.dev>
Reviewed-by: crueter <crueter@eden-emu.dev>

dist/qt_themes/default/style.qss

@@ -509,6 +509,8 @@ QWidget#contentRichDialog QLabel#label_title_rich {
 }
 
 QWidget#contentDialog QLabel#label_dialog {
+    background: #2E2E2E;
+
     padding: 20px 65px;
 }