This is not as straightforward as one would assume. If you try to compare the value of the date field to the @now variable, it doesn't work. You have to do a bit of comparison with subtracting milliseconds from the @now. I had a date field called 'Est DC' in a SharePoint list, see below for my solution.
{
"$schema": "https://developer.microsoft.com/json-schemas/sp/column-formatting.schema.json",
"additionalRowClass": "=if([$Est_x0020_DC] <= @now && [$Est_x0020_DC] >= @now - 86400000, 'sp-field-severity--good', '')"
}
Hope that helps someone.
