hugo-theme-hello-friend/source/css/code.css

.collapsable-code {
  position: relative;
  width: 100%;
  margin: 40px 0;

  input[type="checkbox"] {
    position: absolute;
    visibility: hidden;
  }

  input[type="checkbox"]:checked {
    ~ pre,
    ~ .code-toolbar pre {
      height: 0;
      padding: 0;
      border-top: none;
    }

    ~ .code-toolbar {
      padding: 0;
      border-top: none;

      .toolbar {
        display: none;
      }
    }

    ~ label {
      border-radius: 10px;
    }

    ~ label .collapsable-code__toggle:after {
      content: attr(data-label-expand);
    }
  }

  label {
    position: relative;
    display: flex;
    justify-content: space-between;
    background: hsla(0, 0%, 10%, 10%);
    padding: 10px;
    border-top-left-radius: 10px;
    border-top-right-radius: 10px;
    min-width: 30px;
    min-height: 30px;
    margin: 0;
    cursor: pointer;

    .dark-theme & {
      background: hsla(0, 0%, 10%, 40%);
    }
  }

  &__title {
    flex: 1;
    color: var(--accent);
    padding: 3px 10px;
    text-overflow: ellipsis;
    white-space: nowrap;
    overflow: hidden;
  }

  &__language {
    background: hsl(0, 0%, 100%);
    color: var(--accent);
    border-radius: 10px;
    text-transform: uppercase;
    padding: 3px 10px;

    .dark-theme & {
      background: hsla(0, 0%, 100%, 10%);
    }
  }

  &__toggle {
    color: var(--accent);
    font-size: 16px;
    padding: 3px 10px;

    &:after {
      content: attr(data-label-collapse);
    }
  }

  pre {
    margin-top: 0;
    border-top-left-radius: 0;
    border-top-right-radius: 0;

    &::first-line {
      line-height: 0;
    }
  }

  code {
    &::first-line {
      line-height: 0;
    }
  }

  .code-toolbar {
    margin: 0;
  }
}