grafana/public/sass/components/_form_select_box.scss

$select-input-height: 35px;
$select-input-bg-disabled: $input-bg-disabled;

@mixin select-control() {
  width: 100%;
  margin-right: $gf-form-margin;
  @include border-radius($input-border-radius-sm);
  background-color: $input-bg;
}

@mixin select-control-focus() {
  border-color: $input-border-focus;
  outline: none;
  $shadow: inset 0 1px 1px rgba(0, 0, 0, 0.075), 0 0 8px $input-box-shadow-focus;
  @include box-shadow($shadow);
}

.gf-form-select2__control {
  @include select-control();
  border: 1px solid $input-border-color;
  color: $input-color;
  cursor: default;
  display: table;
  border-spacing: 0;
  border-collapse: separate;
  height: $select-input-height;
  outline: none;
  overflow: hidden;
  position: relative;
}

.gf-form-select2__control--is-focused {
  background-color: $input-bg;
  @include select-control-focus();
}

.gf-form-select2__control--is-disabled {
  background-color: $select-input-bg-disabled;
}

.gf-form-select2__control--menu-right {
  .gf-form-select2__menu {
    right: 0;
    left: unset;
  }
}

.gf-form-select2__input {
  position: absolute;
  z-index: 1;
  top: 0;
  left: 0;
  right: 0;
  padding: 8px 10px;
}

.gf-form-select2__menu {
  background: $select-input-bg-disabled;
  position: absolute;
  z-index: 2;
}

.gf-form-select2__option {
  border-left: 2px solid transparent;

  &.gf-form-select2__option--is-focused,
  &.gf-form-select2__option--is-selected {
    background-color: $dropdownLinkBackgroundHover;
    color: $dropdownLinkColorHover;
    @include left-brand-border-gradient();
    .fa {
      color: $white;
    }
  }
}

.gf-form-select2__value-container {
  display: table-cell;
  padding: 8px 10px;
}

.gf-form-select2__indicators {
  display: table-cell;
  vertical-align: middle;
  padding-right: 5px;
  width: 25px;
}

.gf-form-select2__select-arrow {
  border-color: $white transparent transparent;
  border-style: solid;
  border-width: 5px 5px 2.5px;
  display: inline-block;
  height: 0;
  width: 0;
  position: relative;

  &.gf-form-select2__select-arrow--reversed {
    border-color: transparent transparent $white;
    top: -2px;
    border-width: 0 5px 5px;
  }
}
.gf-form-input--form-dropdown {
  padding: 0;
  border: 0;
  overflow: visible;
}