[Theme Horse Support Team]

Hi Phuong,

Go to Appearance -> Theme Options -> Design Options Tab -> Custom CSS paste the following CSS code and Click on save all changes button:

#access ul li ul li a,
#access ul li.current-menu-item ul li a,
#access ul li ul li.current-menu-item a,
#access ul li.current_page_ancestor ul li a,
#access ul li.current-menu-ancestor ul li a,
#access ul li.current_page_item ul li a {
    font-size: 20px;
}

Thank you!