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');

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