discourse/app/assets/stylesheets/common/select-kit/combo-box.scss

.select-kit {
  &.combo-box {

    .select-kit-body {
      width: 100%;
    }

    .select-kit-row {
      margin: 4px;
      min-height: 1px;
      padding: 4px;
    }

    .select-kit-filter {
      line-height: $line-height-medium;
      padding: 5px 6px;
      border-top: 1px solid dark-light-diff($primary, $secondary, 90%, -60%);
      border-bottom: 1px solid dark-light-diff($primary, $secondary, 90%, -60%);

      .filter-input {
        margin-right: 5px;
      }
    }

    .select-kit-header {
      background: $secondary;
      border: 1px solid $primary-medium;
      padding: 4px;
      font-weight: 500;
      font-size: $font-0;
      line-height: $line-height-large;

      &.is-focused {
        border: 1px solid $tertiary;
        box-shadow: shadow("focus");
      }
    }

    &.is-disabled {
      .select-kit-header {
        background: #e9e9e9;
        border-color: #ddd;
      }
    }

    &.is-highlighted {
      .select-kit-header {
        border: 1px solid $tertiary;
        box-shadow: shadow("focus");
      }
    }

    &.is-expanded {
      .select-kit-wrapper {
        display: block;
        border: 1px solid $tertiary;
        box-shadow: shadow("focus");
      }

      .select-kit-header {
        border-color: transparent;
        box-shadow: none;
      }

      .select-kit-body {
        border-radius: 0 0 3px 3px ;
      }
    }

    &.is-expanded.is-above {
      .select-kit-header {
        border-radius: 0 0 3px 3px;
      }

      .select-kit-body {
        border-radius: 3px 3px 0 0;
      }
    }
  }
}