stepic.js

var $lessonWrapper = $('.course-wrap .lesson-wrapper');

// prevent default animation of right part
$lessonWrapper.css('webkitTransform', 'translateX(0px)');

// allow smooth resizing (just filling with default css value for attribute 'position')
$lessonWrapper.css('position', 'static');

// allow padding animation
$lessonWrapper.css('webkitTransition', 'padding 0.3s');

// force scrollbar to disable animation tilting
$('.course-inner').css('overflowY', 'scroll');

var $toggleButton = $('.toggle-sidebar'),
 	$courseWrap = $('.course-wrap'),
 	toggleButtonLeft = parseInt($toggleButton.css('left'));

// allow toggle position animation
$toggleButton.css('webkitTransition', 'left 0.3s');

$toggleButton.on('click', function(ev) {
	var enabled = $courseWrap.hasClass('with-menu'),
		offset = enabled === true ? 0 : 240;
	$lessonWrapper.css('paddingLeft', offset + 'px');
	$toggleButton.css('left', toggleButtonLeft + offset + 'px');
});