Update rows example to meet accessibility standards

[jazminorozco]

Describe the bug
The example for our rows documentation does not meet accessibility standards. The color of the text on top of the columns does not contrast with the background of the columns.

To Reproduce
Steps to reproduce the behavior:

1. Go to https://denali-design.github.io/denali-css/?path=/story/layouts-rows--playground
2. Look at the example

Expected behavior
Update either the background or the text so that the minimum contrast ratio is met. To test this use a contrast checker such as https://accessible-colors.com/

Screenshots