Hi there,
in your CSS change this:
.main-navigation .main-nav ul li.nav-button a {
background-color: #ff1e00;
border: 2px solid #ff1e00;
border-radius: 40px;
color: #ffffff !important;
line-height: 35px;
}
to:
.main-navigation .main-nav ul li.nav-button a,
.header-wrap #site-navigation:not(.toggled) .main-nav>ul>li.nav-button[class*="current-menu-"]>a {
background-color: #ff1e00;
border: 2px solid #ff1e00;
border-radius: 40px;
color: #ffffff !important;
line-height: 35px;
}