To handle the responsiveness of the
<li id="login-link">...</li>
element, I suggest duplicating it and creating a class to show/hide them based on a media query. Below is an example of how you could achieve this:
@media only screen and (max-width: 599px) {
.mobile-only {
display: inherit;
}
.desktop-only {
display: none;
}
}
@media only screen and (min-width: 600px) {
.mobile-only {
display: none;
}
.desktop-only {
display: inherit;
}
}
<li id="login-link mobile-only"><a href="javascript:;" onclick="$('#login-link').toggleClass('open');">SIGN IN (MOBILE)</a>
<li id="login-link desktop-only"><a href="signin">SIGN IN (DESKTOP)</a>
You may also want to consider using Bootstrap for implementing such functionality smoothly.