text: let title1 = document.querySelectorAll('.title1');
  let i = 0;
  
  title1.forEach(function(title){
      let index = Math.round(title.textContent.length / 2);
      let letter = title.textContent[index];
  
      letterColor(title, letter, tabColor[i]);
      i++;
      if(i === tabColor.length){
          i = 0;
      }
  });
  
  // return letter who be colored
  function chooseLetter (element){
      let index = Math.round(element.textContent.length / 2);
      let letter = element.textContent[index];
  }
  
  function letterColor(element, letterIndex, colorObj){
      element.innerHTML = element.innerHTML.replace(letterIndex,
           '<span style="color:' + 'rgb(' + colorObj.color1 +
       ',' + colorObj.color2 + ',' + colorObj.color3 + ')' + '">'+ letterIndex +'</span>');
  }