How can we design a custom community template in Salesforce?

Hi,

You can not use Visualforce code in these templates. So themes like (Kokua, Koa, Napili, Aloha) templates let you quickly and easily build a self-service community that gives customer the same visual and functional customer experience weather they use tablet or mobile

Community Builder makes it super easy to customize your community. Simply edit a few of the components to include information about your community, add a few images to extend your branding, and you’re ready to go without any coding.

With community builder Templates you can-:

Easily build a mobile-optimized Community
Apply a color scheme to your Community
Change your header and page background color
Customize your font family (from a drop-down list), font size, and font color

if you want a more customer experience, you can create custom pages, add components to pages, use custom Lightning components, and expose additional Salesforce objects.

Rebrand with Custom Theme Layouts

Theme layout is the top level layout of the template pages. It includes headers, footers, navigations and search. The power of using this is flexibility to customize the header, footers, navigation and provide your community with custom themes.

Developers can implement forceCommunity:themelayout to implement custom branding and themes.

Hope it may helps:

Thanks