kit/assets/flex-kit/flex-other.css

/* flex-delimiter text */

:root {
    --flex-delimiter: ', ';
    --flex-delimiter-index: 0;
}

.flex-delimiter > *:not(:first-child):not(:empty)::before {
    content: var(--flex-delimiter);
    --flex-delimiter-index:1;
}

.flex-delimiter > *:empty + *:not(:empty)::before
{
    content: '';
    --flex-delimiter-index:0;
}

.flex-delimiter > *:not(:empty) ~ *:empty + *:not(:empty)::before
{
    content: var(--flex-delimiter);
    --flex-delimiter-index:1;
}

.flex-delimiter > *:empty {
    display:none;
}