Style polish

[perennialAutodidact]

There are a few style adjustments that need to be made:

• The form steps should be center-justified. On mobile, the button should be centered. On desktop, the button should be right-justified
• The form steps need ~30px of padding (maybe more on desktop) on everything below the progress bar. The progress bar should still extend to the edges
• The button and placeholder text for each step should have a capitalized first letter
• The slider background is hard to read. Let's try making the slider track dark gray and the slider handle the same color blue as player 2's color. If the gray track is weird, we could also try keeping it the current color and adding a border and/or drop shadow to give it some contrast.
• The slider needs min/max labels and to display the current slider value
• The form errors should have a human-readable message. "player1Name must be at least 3 characters" -> "Please enter at least three characters" (this can be done in the Yup validation schema for each step)
• If the form has errors, the form field should render Bootstrap's validation styling
• The form error should have ~10px of top padding to push it down away from the input field
• Form errors should stay left-justified relative to the input field (they do this now, but should continue to do so after centered everything else)