timeline_cell_class

specifies the CSS class that will be applied to the cells of the timeline area

item	Task \| object	either the task's or resource's object assigned to the row
date	Date	the date of a cell

Example

<style>
.weekend{ background: #f4f7f4 !important;}
</style>
 
gantt.templates.timeline_cell_class = function(task,date){
    if(date.getDay()==0||date.getDay()==6){
        return "weekend";
    }
};

Related samples

Highlighting weekends

Details

Note that while using work time calculations, you can use isWorkTime instead of hardcoded values:

gantt.config.work_time = true;
 
gantt.templates.timeline_cell_class = function(task,date){
    if(!gantt.isWorkTime({task:task, date:date}))
        return "weekend";
};