How do I add a header drop-down?
To add headers inside the dropdown menu, use the . dropdown-header class in Boostrap. The . dropdown-menu class is used to add a dropdown menu.
How do I split a table header in HTML?
Use an extra column in the header, and use <colspan> in your header to stretch a cell for two or more columns. Insert a <table> with 2 columns inside the td you want extra columns in.