style.css

@import url('https://fonts.googleapis.com/css2?family=Poppins:wght@400;500&display=swap');

* {
  box-sizing: border-box;
}

body {
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  background-color: darkslategray;
  font-family: 'Poppins', sans-serif;
}

ul {
  width: max(500px, 40vw);
  list-style-type: none;
  margin: 0;
  padding: 0;
  max-width: 90vw;
}

li {
  background-color: white;
  padding: 1em;
  margin: 0.5em;
  border-radius: 10px;
}

label {
  display: flex;
  align-items: center;
  justify-content: space-between;
  cursor: pointer;
  font-size: 1.125rem;
  font-weight: bold;
  width: 100%;
  color: red;
  padding: 0.5em;
}

label span {
  transform: rotate(90deg);
}

input[type='radio'] {
  display: none;
}

aside {
  width: 100%;
  max-height: 0px;
  overflow: hidden;
  transition: max-height 300ms ease-in-out;
  padding: 0 0.5em;
}

input[type='radio']:checked + aside {
  max-height: 400px;
}