navigation button layout disappearing after clicking

I have a subscribe button on my primary navigation bar. I have set this button to open a new tab for the subscription page.

The button works okay & a new tab is opening just fine.

but when I am clicking the button the layout of the subscribe button is disappearing from the homepage. when I am clicking the on the page, the button appears again.

Is it possible to stop this disappearing effect?

here is the CSS I am using

@media (min-width: 769px) {
    .main-navigation .main-nav ul li.nav-button a {
        background-color: #ff4e00;
			  border-radius: 30px;
        border: 2px solid #fff;
        color: #fff;
			  transition: 0.3s ease-in-out;
        line-height: 50px !important;
    }
	  .main-navigation .main-nav ul li.nav-button a:hover {
        background-color: #fff;
        border: 2px solid #ff4e00;
        color: #ff4e00;
			  transition: 0.3s ease-in-out;
    }
}