big, small, and color classes

[mbostock]

Adds the following classes (and corresponding CSS custom properties which may be overridden by themes):

• big (--font-big)
• small (--font-color)
• red (--theme-red)
• yellow (--theme-yellow)
• green (--theme-green)
• blue (--theme-blue, formerly --observablehq-blue)
• muted (--theme-foreground-muted)

I chose to use semi-literal color names because sometimes green will mean “good” rather than “positive” (for example, a decline in churn is good).

<div style="max-width: 640px; container-type: inline-size;">
  <div class="grid grid-cols-4">
    <div class="card">
      <h2>GitHub Stars</h2>
      <span class="big">3,541</span>
      <span class="small green">+18 ↗︎</span>
    </div>
    <div class="card">
      <h2>Daily pageviews</h2>
      <span class="big">3,699</span>
      <span class="small green">+2.5% ↗︎</span>
    </div>
    <div class="card">
      <h2>Daily npm downloads</h2>
      <span class="big">2,737</span>
      <span class="small yellow">−33.5% ↘︎</span>
    </div>
    <div class="card">
      <h2>Total npm downloads</h2>
      <span class="big">1,169,127</span>
      <span class="muted">all-time</span>
  </div>
</div>

[Fil]

Concise, and memorable enough to use directly.