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

[ahmadJT]

Description

used background color and opacity without mixin

closes #4236

Markup:

Details

    &.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

• 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)