Got it!
I don’t know if this is really “good coding” but it works so far…
<div
ng-style="{
'background-color': itemValue('Ind_CO2')=='OFF' ? '#223344' : '#223344'
}"
class="template-container"
style="top:0;bottom:0;left:0;right:0;position:absolute">
<div class="template-contents">
<div class="row">
<div class="col-xs-12"><span><widget-icon iconset="'smarthome-set'" icon="'houseplant'" /></span></div>
</div>
<div class="row">
<div class="col-xs-12"><span style="color: #4CC417; font-size: 10pt; text-align:center">{{itemValue('Ind_CO2')| number:0}}<small style="font-size:8pt"></small></span></div>
</div>
</div>
</div>