fix(VaDataTable): use background color and opacity without mixin

[ahmadJT]

Description

used background color and opacity without mixin

closes #4236

Markup:

```vue &.striped { .va-data-table__table-tbody { .va-data-table__table-tr { &:nth-of-type(2n) { &:not(.selected) { td { // Position relative doesn't work on tr in Safari position: relative; background: var(--va-data-table-striped-tr-background-color); opacity: var(--va-data-table-striped-tr-opacity); } } } } } } ```

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] Improvement/refactoring (non-breaking change that doesn't add any feature but make things better)