You can customize the background colour by adding your HEX code of the background colour in your embed code.

<div class="bendigi-calculators"
    apikey="API_KEY"
    terms="https://canadianmortgageapp.com/terms"
    navpositiontop="0px"
    tools="all"
    background="#138F45">
</div>
<script src="https://tools.bendigi.com/assets/calculators.js"></script>