As I can see, you do not use our Header builder and styles come from Elementor plugin – http://prntscr.com/t1xfky
You can create the header from scratch using our builder – https://www.youtube.com/watch?v=RbdKjQrFnO4&list=PLMqMSqDgPNmDu3kYqh-SAsfUqutW3ohlG
or change the styling of current buttons using custom CSS code, for example
.header .elementor-button {
background-color: red;
color: black;
}
.header .elementor-button:hover {
background-color: black;
color: red;
}
Regards