Accordion is not working when I click the button

I’m trying to add the accordion in my page. But when I click the button it’s not toggling.

Here is my Html

var acc = document.getElementsByClassName("accordion");
var i;

for (i = 0; i < acc.length; i++) {
  acc[i].addEventListener("click", function() {
    this.classList.toggle("active");
    var panel = this.nextElementSibling;
    if (panel.style.maxHeight) {
      panel.style.maxHeight = null;
    } else {
      panel.style.maxHeight = panel.scrollHeight + "px";
    }
  });
}

.blks {
  .accordion {
    background-color: #eee;
    color: #444;
    cursor: pointer;
    padding: 18px;
    width: 100%;
    border: none;
    text-align: left;
    outline: none;
    font-size: 15px;
    transition: 0.4s;
    &:after {
      content: '02B';
      color: #777;
      font-weight: bold;
      float: right;
      margin-left: 5px;
    }
    &:hover {
      background-color: #ccc;
    }
  }
  .active {
    background-color: #ccc;
    &:after {
      content: "2212";
    }
  }
  .panel {
    padding: 0 18px;
    background-color: white;
    max-height: 0;
    overflow: hidden;
    transition: max-height 0.2s ease-out;
  }
}

<div class="blks">

  <button class="accordion">Section 1</button>
  <div class="panel">
    <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.</p>
  </div>

  <button class="accordion">Section 2</button>
  <div class="panel">
    <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.</p>
  </div>

  <button class="accordion">Section 3</button>
  <div class="panel">
    <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.</p>
  </div>

</div>

Answer

Your stylesheet is sass/scss and needs to be compiled or translated to plain CSS (which is the answer to your question)

Also I suggest you delegate

document.querySelector(".blks").addEventListener("click", function(e) {
  const tgt = e.target; 
  if (!tgt.matches(".accordion")) return; // not a button
  tgt.classList.toggle("active");
  var panel = tgt.nextElementSibling;
  if (panel.style.maxHeight) {
    panel.style.maxHeight = null;
  } else {
    panel.style.maxHeight = panel.scrollHeight + "px";
  }

});

.blks .accordion {
     background-color: #eee;
     color: #444;
     cursor: pointer;
     padding: 18px;
     width: 100%;
     border: none;
     text-align: left;
     outline: none;
     font-size: 15px;
     transition: 0.4s;
}
 .blks .accordion:after {
     content: '02B';
     color: #777;
     font-weight: bold;
     float: right;
     margin-left: 5px;
}
 .blks .accordion:hover {
     background-color: #ccc;
}
 .blks .active {
     background-color: #ccc;
}
 .blks .active:after {
     content: "2212";
}
 .blks .panel {
     padding: 0 18px;
     background-color: white;
     max-height: 0;
     overflow: hidden;
     transition: max-height 0.2s ease-out;
}
 

<div class="blks">

  <button class="accordion">Section 1</button>
  <div class="panel">
    <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.</p>
  </div>

  <button class="accordion">Section 2</button>
  <div class="panel">
    <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.</p>
  </div>

  <button class="accordion">Section 3</button>
  <div class="panel">
    <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.</p>
  </div>

</div>