[Backport] [Resolved : Styling <select> by changing less variables in Luma theme…

[hitesh-wagento]

Original Pull Request

#15734
Have "select" elements with the styles you set in _theme.less

Description

Fixed Issues (if relevant)

1. magento/magento2#Styling <select> by changing less variables in Luma theme doesn't work as expected #15608 : Issue title Styling select by changing less variables in Luma theme doesn't work as expected

Manual testing scenarios

1. In Custom/theme/web/css/source/_theme.less set less variables:
   @select__background: rgba(255, 255, 255, 0.15);
   @select__border: 2px dashed blue;
   @select__height: 50px;
   @select__padding: 15px 40px 15px 15px;
   @select__background-clip: border-box;
2. Compile less

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[magento-engcom-team]

Hi @hitesh-wagento. Thank you for your contribution.
Changes from your Pull Request will be available with the upcoming 2.1.15 release.