[Theme Horse Support Team]

Hi Phil,

Sorry for that we forget that the character > will not support in the custom CSS for security reason.
So, Now you have to create the child theme and use above override CSS code.

To create the child theme create a new folder name ambition-child.
Also create a style.css inside ambition-child folder and paste the below CSS code:

/*
Theme Name: Ambition Child Theme
Author: Theme Horse WordPress User
Template: ambition
*/
@import url("../ambition/style.css"); 
.main-navigation a:hover,
.main-navigation ul li.current-menu-item a,
.main-navigation ul li.current_page_ancestor a,
.main-navigation ul li.current-menu-ancestor a,
.main-navigation ul li.current_page_item a,
.main-navigation ul li:hover > a,
.main-navigation ul li ul li a:hover,
.main-navigation ul li ul li:hover > a,
.main-navigation ul li.current-menu-item ul li a:hover {
   color: #00ffff;
}

Now activate your child theme ambition-child via dashboard and also do not delete the main theme ambition because it will be a parent theme of your child theme ambition-child.

Hope it will help.

Thank you!