It won’t work like that, the dynamic part you entered won’t be parsed there.
Better is to use a css variable. Example:
In your css have something like:
h5 {
color: var(--heading-color);
}
And on your body tag add:
<body is="dmx-app" id="index" dmx-bind:style="'--heading-color:' + getmyconfig.data.query.primaryColor">