https://marketplace.whmcs.com/product/5055-croster-whmcs-theme
Croster WHMCS Theme - WHMCS Marketplace
Design your own layout with different color schemes for header, footer, navigation bars, sections and pricing tables.
whmcs thememarketplace
https://blog.whmcs.com/133663/theme-and-template-compatibility
Theme and Template Compatibility | WHMCS Blog
themetemplatecompatibilitywhmcsblog