Doc strange outline love (jQuery-free)

header.js

//detecting tab key press
document.body.addEventListener('keydown', function detector (e) {
	var keyCode = e.keyCode || e.which;

	if(keyCode == 9) {
		console.log( 'Tab detected' );

		document.documentElement.className += ' is-keyboarduser';

		document.body.removeEventListener('keydown', detector);
	}
});

mixins.less

.outline() {
	outline: none;

	.is-keyboarduser & {
		outline: 2px dotted #000;
		outline-offset: 0.5rem;
	}
}

tabs.less

.tab-link {
	&:focus {
		.outline();
	}
}

Here's a jQuery-free version: https://gist.github.com/dominikwilkowski/b2b4a766030891b0622e