amis2/scss/components/form/_tree-select.scss

.#{$ns}TreeSelectControl {
  position: relative;

  > .#{$ns}TreeSelect-popover {
    width: 100%;
  }
}

.#{$ns}TreeSelect {
  @include input-text();
  outline: none;

  &.is-opened {
    border-color: var(--Form-input-onFocused-borderColor);
    box-shadow: var(--Form-input-boxShadow);
    background: var(--Form-input-onFocused-bg);
  }

  &-popup {
    height: px2rem(400px);
  }
}

.#{$ns}TreeSelect-popover {
  background: transparent;
  border: none;
  box-shadow: none;

  > .#{$ns}Tree {
    background: var(--TreeSelect-popover-bg);
    border: var(--Form-input-borderWidth) solid
      var(--Form-input-onFocused-borderColor);
    padding: var(--gap-xs) var(--Form-input-paddingX);
    border-radius: 0;
    margin-top: -1px;
    max-height: 400px;
    overflow: auto;
  }
}