Thank you for posting here in the Community. It's my pleasure to share some information about customizing form styles in QuickBooks Online (QBO).
We can customize styles by importing custom form styles to QBO. We can import styles by going to the Gear icon, selecting Custom Form Styles under YourCompany, clicking the New style drop-down arrow and selecting Import style. However, we don't have the option to import purchase order form.
Since this option isn't available in QBO as of the moment, I suggest sending this idea to our product engineers for future updates. To send your product suggestions/feedback:
Go to the Gear icon.
Share your product suggestions/feedback in the Feedback page.
Click Next and send your message.
That would let you send your suggestions to our product developers. Feel free to add a comment if you have any other questions about creating purchase orders. Have a wonderful day!