edoobix

var box=document.getElementsByClassName('certificates-item');
        var btn=document.getElementById('button');
        for (let i=10;i<box.length;i++) {
            box[i].style.display = "none";
        }

        var countD = 10;
        btn.addEventListener("click", function() {
            var box=document.getElementsByClassName('certificates-item');
            countD += 10;
            if (box.length <= countD){
                for(let i=0;i<countD;i++){
                    if(box[i]){
                      box[i].style.display = "block";
                    }
                }
            }
        })