Edit in JSFiddle

var json = {
    "completedHtml": "<h3>Thank you for your feedback.</h3> <h5>Your thoughts and ideas will help us to create a great product!</h5>",
    "completedHtmlOnCondition": [
        {
            "expression": "{nps_score} > 8",
            "html": "<h3>Thank you for your feedback.</h3> <h5>We glad that you love our product. Your ideas and suggestions will help us to make our product even better!</h5>"
        }, {
            "expression": "{nps_score} < 7",
            "html": "<h3>Thank you for your feedback.</h3> <h5> We are glad that you share with us your ideas.We highly value all suggestions from our customers. We do our best to improve the product and reach your expectation.</h5>\n"
        }
    ],
    "pages": [
        {
            "name": "page1",
            "elements": [
                {
                    "type": "rating",
                    "name": "nps_score",
                    "title": "On a scale of zero to ten, how likely are you to recommend our product to a friend or colleague?",
                    "isRequired": true,
                    "rateMin": 0,
                    "rateMax": 10
                }, {
                    "type": "checkbox",
                    "name": "promoter_features",
                    "visibleIf": "{nps_score} >= 9",
                    "title": "What features do you value the most?",
                    "isRequired": true,
                    "validators": [
                        {
                            "type": "answercount",
                            "text": "Please select two features maximum.",
                            "maxCount": 2
                        }
                    ],
                    "hasOther": true,
                    "choices": [
                        "Performance", "Stability", "User Interface", "Complete Functionality"
                    ],
                    "otherText": "Other feature:",
                    "colCount": 2
                }, {
                    "type": "comment",
                    "name": "passive_experience",
                    "visibleIf": "{nps_score} > 6  and {nps_score} < 9",
                    "title": "What is the primary reason for your score?"
                }, {
                    "type": "comment",
                    "name": "disappointed_experience",
                    "visibleIf": "{nps_score} notempty",
                    "title": "What do you miss and what was disappointing in your experience with us?"
                }
            ]
        }
    ],
    "showQuestionNumbers": "off"
};

Survey.defaultBootstrapCss.navigationButton = "btn btn-green";
Survey.defaultBootstrapCss.matrixdynamic.button = "btn btn-green";

var survey = new Survey.Model(json);

survey.onComplete.add(function(result) {
	document.querySelector('#result').innerHTML = "result: " + JSON.stringify(result.data);
});

$("#surveyElement").Survey({
  model: survey
});
<div id="surveyElement"></div>

<div id="result"></div>
.btn-green {
  background-color: #1ab394;
  color: #fff;
  border-radius: 3px;
  
  &:hover, &:focus {
    background-color: #18a689;
    color: #fff;
  }
}

.panel-footer {
    text-align: right;
    background-color: #fff;
}