Hello digang,
=> Put below css code into Additional CSS textarea (Dashboard >> Apperance >> Customize) then click on Save & Publish button.
=> If there is no Additional CSS option then put below css code into your current theme’s style.css file located at wp-content/themes/your_current_active_theme/ folder.
.menus {
background: #ddd;
}
#site-navigation li:hover {
background: #F94B71 ;
}
.menus li a {
color: #81B541 ;
}
.menus li a:hover {
color: #888;
}
Note : All Changes you done in style.css or other file are gone when you update theme. So prefer Child Theme
Hope this will helps you.