text: (function(){
     "use strict";
  
     let btn = document.querySelectorAll('.btn');
     let contentOne = document.querySelectorAll('.contents .content-one');
     let btnOne = document.querySelectorAll('.tab .btn-one');
  
          btnOne.forEach(function(el){
              el.style.backgroundColor = 'rgb(59, 59, 61';
              el.style.color = 'white';
          });  
          
          contentOne.forEach(function(el){
              el.style.display = 'block';
          });
  
       btn.forEach(function (el){  
          el.addEventListener('click' , function(e){
              
           let btnOne = this.parentElement.parentElement.children[0].children[0];
           let btnTwo = this.parentElement.parentElement.children[1].children[0];
           let btnThree = this.parentElement.parentElement.children[2].children[0];
           let btnFour = this.parentElement.parentElement.children[3].children[0];
           let btns = [btnOne, btnTwo, btnThree, btnFour];
          
          btns.forEach(function(el){
              el.style.backgroundColor = 'beige';
              el.style.color = 'rgb(59, 59, 61';   
          });    
          this.style.backgroundColor = 'rgb(59, 59, 61';
          this.style.color = 'white';
        
          let contents = this.parentElement.parentElement.children[4];
         
          switch(this.classList[0]){
              case "btn-one":
              contents.children[0].style.display = 'block'
              contents.children[1].style.display = 'none'
              contents.children[2].style.display = 'none'
              contents.children[3].style.display = 'none'
              break;
              case "btn-two":
              contents.children[0].style.display = 'none'
              contents.children[1].style.display = 'block'
              contents.children[2].style.display = 'none'
              contents.children[3].style.display = 'none'
              break;
              case "btn-three":
              contents.children[0].style.display = 'none'
              contents.children[1].style.display = 'none'
              contents.children[2].style.display = 'block'
              contents.children[3].style.display = 'none'
              break;
              case "btn-four":
              contents.children[0].style.display = 'none'
              contents.children[1].style.display = 'none'
              contents.children[2].style.display = 'none'
              contents.children[3].style.display = 'block'
              break;
              default:
                return false;
          }
         }); 
     })
  })();