[Bug]: clear_button not shown correclty for "Select Multiple" inputs using default theme

[ksouthworth]

Bug description

The clear_button is shown as a blue outlined box, and the "x" icon is not visible due to a CSS issue in the default theme.
You can see it on the examples page for the plugin:
https://tom-select.js.org/plugins/clear-button/

Expected behavior

Expect to see a visible button with the "x" visible, something like this:

Steps to reproduce

1. Go to https://tom-select.js.org/plugins/clear-button/
2. Changes the theme in the upper right to "Theme: Default"
   ...
   X. See error

Additional context

All platforms