pico/scss/components/_dropdown.scss

details[role="list"] {
  position: relative;
  padding: 0;
  border-bottom: none;

  summary {
    margin: 0;

    &:not([role="button"]) {
      height: calc(
        1rem * var(--line-height) + var(--form-element-spacing-vertical) * 2 +
          var(--border-width) * 2
      );
      padding: var(--form-element-spacing-vertical) var(--form-element-spacing-horizontal);
      border: var(--border-width) solid var(--form-element-border-color);
      border-radius: var(--border-radius);
      background-color: var(--form-element-background-color);
      color: var(--form-element-placeholder-color);
      line-height: inherit;
      cursor: pointer;

      @if $enable-transitions {
        transition: background-color var(--transition),
          border-color var(--transition), color var(--transition),
          box-shadow var(--transition);
      }

      // Active & Focus
      &:active,
      &:focus {
        border-color: var(--form-element-active-border-color);
        background-color: var(--form-element-active-background-color);
      }

      // Focus
      &:focus {
        box-shadow: 0 0 0 var(--outline-width) var(--form-element-focus-color);
      }

      // Marker
      &::after {
        height: 100%;
      }
    }

    & + ul {
      z-index: 99;
      position: absolute;
      top: auto;
      right: 0;
      left: 0;
      margin: 0;
      padding: 0;
      border: var(--border-width) solid var(--dropdown-border-color);
      border-top: none;
      border-radius: var(--border-radius);
      border-top-right-radius: 0;
      border-top-left-radius: 0;
      background-color: var(--dropdown-background-color);
      box-shadow: var(--card-box-shadow);
      color: var(--dropdown-color);

      li {
        margin-bottom: 0;
        padding: calc(var(--form-element-spacing-vertical) * 0.5) var(--form-element-spacing-horizontal);
        list-style: none;

        &:first-of-type {
          margin-top: calc(var(--form-element-spacing-vertical) * 0.5);
        }

        &:last-of-type {
          margin-bottom: calc(var(--form-element-spacing-vertical) * 0.5);
        }

        &:hover {
          background-color: var(--dropdown-focus-background-color);
        }

        a {
          display: block;
          width: 100%;
          color: var(--dropdown-color);
          text-decoration: none;
        }
      }
      
    }

    &::after {
      transform: rotate(0deg);
    }
  }

  &[disabled] summary,
  &.disabled summary {
    border-color: var(--form-element-disabled-border-color);
    background-color: var(--form-element-disabled-background-color);
    opacity: var(--form-element-disabled-opacity);
    pointer-events: none;
  }

  &[open] summary {
    border-bottom-right-radius: 0;
    border-bottom-left-radius: 0;
    &::before {
      display: block;
      z-index: 1;
      position: fixed;
      top: 0;
      right: 0;
      bottom: 0;
      left: 0;
      background: transparent;
      content: '';
      cursor: default;
    }
  }
}