Thank you for contacting Syncfusion support.
Based on provided information we understood you are adding SfForm into TabPageAdv in run time, we tried to replicate same in a simple sample.
Firstly, we have added a TagPageAdv in designer and then added the SfForm in constructor and then with a button click we have added a new TabPageAdv with SfForm. Comparing the both we noticed a color difference in right border. But the theme was applied properly to both SfForm and SfNumericTextBox.
Please refer the image below.
Image 1: TabPageAdv added in designer
Image 2: TabPageAdv added in button click
Please let us know if this is the issue you are concerned or if you have any different issue, please modify the sample based on your scenario.
Regards,
Nikhilesh O