Smooth Responsive Accordion UI

A responsive, nice-looking accordion UI with smooth transitions. Built with HTML, CSS (SCSS), and a little bit of JavaScript.

How to use it:

1. The HTML structure for the accordion UI.

<section class="accordion container">
  <div class="accordion__container">
    <div class="accordion__item">
      <header class="accordion__header">
        <i class="bx bx-plus accordion__icon"></i>
        <h3 class="accordion__title">What"s an accordion?</h3>
      </header>
      <div class="accordion__content">
        <p class="accordion__description">
          An accordion always contains the category title, an expanded and a collapsed state, 
          an icon indicating expansion, and the spacing between them.
        </p>
      </div>
    </div>
    <div class="accordion__item">
      <header class="accordion__header">
        <i class="bx bx-plus accordion__icon"></i>
        <h3 class="accordion__title">When and how should it be used?</h3>
      </header>
      <div class="accordion__content">
        <p class="accordion__description">
          It should be used when users only need a few key concepts or descriptions 
          of the content on a single page.
        </p>
      </div>
    </div>
    <div class="accordion__item">
      <header class="accordion__header">
        <i class="bx bx-plus accordion__icon"></i>
        <h3 class="accordion__title">What happens if the user clicks on a collapsed card while another card is open?</h3>
      </header>
      <div class="accordion__content">
        <p class="accordion__description">
          It happens that the open card was closed, to give way to the information of the next 
          open card, but there are different designs that prefer it the other way around.
        </p>
      </div>
    </div>
    <div class="accordion__item">
      <header class="accordion__header">
        <i class="bx bx-plus accordion__icon"></i>
        <h3 class="accordion__title">How to choose an icon to indicate expansion?</h3>
      </header>
      <div class="accordion__content">
        <p class="accordion__description">
          You must choose a different icon to open and close, so that the user 
          understands what action he took.
        </p>
      </div>
    </div>
  </div>
</section>

2. The main CSS styles for the accordion UI.

:root {
  /*========== Colors ==========*/
  --hue-color: 225;
  --first-color: hsl(var(--hue-color), 48%, 35%);
  --title-color: hsl(var(--hue-color), 48%, 22%);
  --text-color: hsl(var(--hue-color), 12%, 35%);
  --body-color: hsl(var(--hue-color), 49%, 98%);
  --container-color: #FFF;
  /*========== Font and typography ==========*/
  --body-font: 'Poppins', sans-serif;
  --normal-font-size: .938rem;
  --small-font-size: .813rem;
  --smaller-font-size: .75rem;
}
.accordion {
  display: grid;
  align-content: center;
  height: 100vh;
}
.accordion__container {
  display: grid;
  row-gap: .75rem;
  padding: 2rem 1rem;
  background-color: var(--container-color);
  border-radius: .5rem;
  box-shadow: 0 12px 32px rgba(51, 51, 51, 0.1);
}
.accordion__title {
  font-size: var(--small-font-size);
  color: var(--title-color);
  font-weight: 400;
  margin-top: .15rem;
  transition: .2s;
}
.accordion__header {
  display: flex;
  column-gap: .5rem;
  padding: 1.25rem 1.25rem 1.25rem 1rem;
  cursor: pointer;
}
.accordion__description {
  padding: 0 1.25rem 1.25rem 3rem;
  font-size: var(--smaller-font-size);
}
.accordion__icon {
  font-size: 1.5rem;
  height: max-content;
  color: var(--title-color);
  transition: .3s;
}
.accordion__item {
  box-shadow: 0 2px 6px rgba(38, 38, 38, 0.1);
  background-color: var(--container-color);
  border-radius: .25rem;
  position: relative;
  transition: all .25s ease;
}
.accordion__item::after {
  content: '';
  background-color: var(--first-color);
  width: 5px;
  height: 100%;
  position: absolute;
  top: 0;
  left: 0;
  border-radius: .25rem 0 0 .25rem;
}
.accordion__item:nth-child(1) {
  background-color: #fff7f0;
}
.accordion__item:nth-child(1)::after {
  background-color: #ffc08a;
}
.accordion__item:nth-child(2) {
  background-color: #f0f0ff;
}
.accordion__item:nth-child(2)::after {
  background-color: #8a8aff;
}
.accordion__item:nth-child(3) {
  background-color: #fff0f3;
}
.accordion__item:nth-child(3)::after {
  background-color: #ff8aa1;
}
.accordion__item:nth-child(4) {
  background-color: #f0faff;
}
.accordion__item:nth-child(4)::after {
  background-color: #8ad8ff;
}
.accordion__content {
  overflow: hidden;
  height: 0;
  transition: all .25s ease;
}
/*Rotate icon and add font weight to titles*/
.accordion-open .accordion__icon {
  transform: rotate(45deg);
}
.accordion-open .accordion__title {
  font-weight: 600;
}

3. Make the accordion fully responsive so that it works perfectly on any devices like desktop and mobile.

/*=============== MEDIA QUERIES ===============*/
/* For medium devices */
@media screen and (min-width: 576px) {
  .accordion__container {
    width: 550px;
    padding: 2.5rem;
    justify-self: center;
    border-radius: .75rem;
  }
  .accordion__header {
    padding: 1.5rem;
  }
  .accordion__title {
    padding-right: 3.5rem;
  }
  .accordion__description {
    padding: 0 4rem 1.25rem 3.5rem;
  }
}
/* For large devices */
@media screen and (min-width: 968px) {
  .container {
    margin-left: auto;
    margin-right: auto;
  }
}

4. The main JavaScript to enable the accordion logic.

const accordionItems = document.querySelectorAll('.accordion__item')
accordionItems.forEach((item) =>{
  const accordionHeader = item.querySelector('.accordion__header')
  accordionHeader.addEventListener('click', () =>{
      const openItem = document.querySelector('.accordion-open')
      toggleItem(item)
      if(openItem && openItem!== item){
          toggleItem(openItem)
      }
  })
})
const toggleItem = (item) =>{
  const accordionContent = item.querySelector('.accordion__content')
  if(item.classList.contains('accordion-open')){
      accordionContent.removeAttribute('style')
      item.classList.remove('accordion-open')
  }else{
      accordionContent.style.height = accordionContent.scrollHeight + 'px'
      item.classList.add('accordion-open')
  }
}