Use all dropdowns CSS variables

Description

This PR is a proposal to use all dropdowns CSS variables available:

• --#{$variable-prefix}dropdown-inner-border (that probably needed to be renamed in --#{$variable-prefix}dropdown-inner-border-radius since it is based on $dropdown-inner-border-radius)
• --#{$variable-prefix}dropdown-divider-margin-y

Motivation & Context

--#{$variable-prefix}dropdown-inner-border and --#{$variable-prefix}dropdown-divider-margin-y were not used in the _dropdown.scss file.

Types of changes

• Refactoring (non-breaking change)

Checklist

• I have read the contributing guidelines
• My code follows the code style of the project (using npm run lint)
• My change introduces changes to the documentation
• I have updated the documentation accordingly
• I have added tests to cover my changes
• All new and existing tests passed

Related issues

N/A

Live preview