That was quick!
In the meantime I just finished a workaround ![]()
Leaving the code below just in case.
var categoryBoxes = document.getElementsByClassName('category-box');
for (var i = 0; i < categoryBoxes.length; i++) {
var categoryBox = categoryBoxes[i];
var dataCategoryId = categoryBox.getAttribute('data-category-id');
categoryBox.style.border = '2px solid var(--category-' + dataCategoryId + '-color)';
}