Here is a custom code to change the color of the ““Feature grid with box and three column view” block’s containers.
Please add the code to the Page settings → Custom code header section, make sure you change the feature-grid1 text to the ID of your feature grid block and save and publish the app.
<style>
#feature-grid1 .feature-container .feature-box {
background: #ff00ff!important;
}
</style>