HTML

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<section class="accordion">
  <div class="tab">
 
 
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CSS

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:root {
  --primary: #ff5252;
 
 
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JS

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:root {
  --primary: #ff5252;
  --background: #eee;
  --highlight: #ffda79;
  --theme: var(--primary);
}

*, *::before, *::after {
  box-sizing: border-box;
}

body {
  display: grid;
  place-content: center;
  grid-template-columns: repeat(auto-fit, min(100%, 30rem));
  min-height: 100vh;
  place-items: start;
  gap: 1rem;
  margin: 0;
  padding: 1rem;
  background: var(--background);
}

.tab input {
  position: absolute;
  opacity: 0;
  z-index: -1;
}

.accordion-tab-content {
  max-height: 0;
  overflow: hidden;
  transition: all 0.35s;
}

.tab input:checked ~ .accordion-tab-content {
  max-height: 10rem;
}

.accordion {
  --theme: var(--primary);
  color: var(--theme);
  border: 2px solid;
  border-radius: 0.5rem;
  overflow: hidden;
}

.accordion-tab-label {
  display: flex;
  color: white;
  background: var(--theme);
  cursor: pointer;
}

.accordion-tab-label {
  justify-content: space-between;
  padding: 1rem;
}

.accordion-tab-label::after {
  content: "\276F";
  width: 1em;
  height: 1em;
  text-align: center;
  transform: rotate(90deg);
  transition: all 0.35s;
}

.tab input:checked + .accordion-tab-label::after {
  transform: rotate(270deg);
}

.accordion-tab-content p {
  margin: 0;
  padding: 1rem;
}

.tab input:not(:checked) + .accordion-tab-label:hover::after {
  animation: bounce .5s infinite;
}

@keyframes bounce {
  25% {
    transform: rotate(90deg) translate(.25rem);
  }
  75% {
    transform: rotate(90deg) translate(-.25rem);
  }
}

Pure CSS Accordion with Radio Button

100% pure CSS accordion built with radio button.

f you want to expand more than one tab, you can change radio button to checkbox. You can see a reference here Multi-Open Accordion with Checkbox.