I know only one way - download and install this plugin: scirra.com/forum/plugin-call-javascript_topic45866.html, then write script like this:
(function autorun() {
$("head").append("<link rel='stylesheet' type='text/css' href='https://dl.dropboxusercontent.com/u/7329218/myStyle.css' />");
})();
CSS source:
— {
font-family: 'Press Start 2P';
font-style: normal;
font-weight: 400;
src: local('Press Start 2P'), local('PressStart2P-Regular'), url(http://themes.googleusercontent.com/static/fonts/pressstart2p/v1/8Lg6LX8-ntOHUQnvQ0E7o_2ShpZkVnhIV7pxLwZ7Eps.woff) format('woff');
}
input {
font-family: 'Press Start 2P';
}