hamburger menu color not changing

I'm trying to update ONLY the hamburger icon color to white without it effecting the color settings I have in place for the menu text. I've added this but it's not working. The hamburger menu is currently green (#44b251) because the menu text is set to that..... you can't see the hamburger icon becuase my top bar background color is the same #44b251.

@media (max-width: 768px) {
button.menu-toggle {
position: fixed;
right: 5px;
top: 5px;
text-align: left;
font-size:19px;
color:#ffffff;
}
button.menu-toggle:hover {
color:#ffffff;
}
button.menu-toggle:visited {
color:#ffffff;
}
}