How to find the hightlight CSS of task?

[zhysimon]

If I click the task whose edge looked not very clearly.

[ramil]

Hello,
You can use the gantt_selected selector for the selected tasks. To affect the task bars in the timeline, you need to use the gantt_task_line selector:

You can read more about selectors in the following article:

CSS Documentation | DHTMLX Gantt Docs