Hello there, Asim.

Welcome to the Community.

To change or add a custom style for invoices, you can navigate directly to the Custom Form Style section. Here's how:

1. Click the Gear icon.
2. Under Lists, select All lists.
3. Locate Custom Form Styles and click it.
4. In the upper-right corner, select the New style drop-down, then choose Invoice.
5. Under the Design section:
   • Edit or modify the name of the invoice template.
   • Select Change up template to choose your desired invoice style.
   • You can also add a logo, change the colours, and select a different font style.
6. Click Content if you'd like to customise the details and content of your invoice.
7. Once you're satisfied with the design of your invoice, click Done.

Now you have multiple custom form styles available for your invoice. Check the sample screenshot below for reference.

For more detailed instructions on customising your invoice templates, please refer to this article: Customise Invoices, Estimates, and Sales Receipts in QuickBooks Online.

If you have any questions or need additional assistance, the Community is always here to help.