[BUG] Exporting via reporting on dark mode broke

[BT-93]

When dark mode is set and you export to either PNG or PDF the background of the exports is white.
This was not an issue prior to version 2.6 (I think).

To Reproduce
Steps to reproduce the behavior:

1. Go to Advanced Settings
2. Search for Dark Mode
3. Set the slider to Dark Mode
4. Go to a dashboard
5. Select Reporting
6. Go either PNG or PDF
7. Exported doco background is white

Expected behavior
The background to be color #141519

OpenSearch Version
2.6 & 2.7

Dashboards Version
2.6 & 2.7

Plugins
The default ones

Screenshots

Host/Environment (please complete the following information):

• OS: Windows 10
• Browser and version: Chrome Version 113.0.5672.64 (Official Build) (64-bit)

Additional context
:)

[zhongnansu]

@opensearch-project/triage Please transfer this issue to reporting repo https://github.com/opensearch-project/dashboards-reporting

[kavilla]

Issue moved to opensearch-project/dashboards-reporting #111.