Add this code to the Custom CSS field on the Style tab of your Instagram Feed widget’s settings:
.es-load-more-button {
background-color: rgb(211, 13, 125);
}
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:
.es-load-more-button {
background-color: rgb(211, 13, 125);
}
Let us know if the solution worked for you