Originated from this comment in #6850

There are a few accessibility enhancements to be made with EuiSteps and EuiStepsHorizontal. Each is described below.

1. Add a halo to the current step

The current (blue) dot is very similar in hue and intensity to the completed (green) steps. The completed steps do have a black check mark, but at small size I'm not sure this is enough to meet the requirements of SC 1.4.1: Use of Color (Level A). I'd recommend adding a differentiation to the current step, like a bold outer halo of the same color with 2-4px of whitespace between the dot and the outer border.

Proposed solution: Add a halo to the current step that matches its primary color. This change should not be applied to any other status.

2. Update disabled text color to meet 4:5.1 contrast ratio (for light mode and dark mode)
   The current coloring of step titles that are disabled do not currently have a good contrast ratio. Let's use a color utility to increase the contrast on the text for better visibility.