chromium/third_party/blink/renderer/core/html/resources/stylable_select_linux.css

/* Copyright 2024 The Chromium Authors
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 *
 * The default style sheet used to render <select> when the StylableSelect
 * feature is enabled and the platform is Linux. It can be merged into
 * linux.css when StylableSelect is enabled and the flag is removed.
 */

/* This sheet is appended to LayoutTheme::ExtraDefaultStyleSheet() before
   parsing which means the selectors below are in the default html namespace:

   @namespace "http://www.w3.org/1999/xhtml"
*/

select:not(:-internal-list-box) {
    /* Selects with popup menus look like buttons with a drop down triangle on Linux. */
    background-color: -internal-appearance-auto-base-select(ButtonFace, transparent);
}