Add this code to the Custom CSS field on the Style tab of your Instagram Feed widget’s settings:
.global-styles, .es-popup-close::before, .es-popup-close::after{
background: rgb(0, 0, 0) !important;
}
Let us know if the solution worked for you 
Add this code to the Custom CSS field on the Style tab of your Instagram Feed widget’s settings:
.global-styles, .es-popup-close::before, .es-popup-close::after{
background: rgb(0, 0, 0) !important;
}
Let us know if the solution worked for you