For text color and background color:
Go to Customizer > Colors > Primary Navigation > Navigation Search.
For the active search bar background color:
Go to Customizer > Additional CSS. Find the css start with this selector .navigation-search.nav-search-active
, change the color code there.
https://www.screencast.com/t/0aeMdHyADC
For font and border try this CSS.
.navigation-search input[type="search"] {
font-family: 'dashicons';
border: 2px solid #FFF;
}
Let me know π