Could you please share a bit more about your issue?
Do you mean that there is something issue with the padding property within the DatePicker control in your custom form?
Further, could you please share more details about the Padding properties (Padding Top, Padding Bottom, Padding Left and Padding Right) of the DatePicker control in your app?
I have made a test on my side, and don't have the issue that you mentioned. Please check if the Padding Top property and Padding Bottom property of the DatePicker control is set to same value.
Please take a try to set the the Padding Top property and Padding Bottom property of the DatePicker control to 0.
In addition, please consider take a try to turn off/disable the "Improved app rendering (final validation)" option within Advanced settings of App seetings of your app, re-publish your app, check if the issue is soloved.
If the issue still exists, please consider take a try to remove the custom form from your SP list, then re-add a new one for it, check if the issue still exists. Also please take a try to run your custom form within other different browsers, then check if the issue still exists.
Community Support Team _ Kris Dai If this post helps, then please consider Accept it as the solution to help the other members find it more quickly.