Contrast issues on Examples page

[RaphGL]

Hey, I was going through the Examples page today and noticed that the text wasn't showing up correctly on one of the examples so I went through the entire page looking for contrast issues. Here's what I found:

On dark mode

• Numbers are dark after typing on keyboard:
  https://svelte.dev/examples/component-bindings

• Both the button and the text is white but their hover style is fine:
  https://svelte.dev/examples/easing

• Text is too dark
  https://svelte.dev/examples/area-chart

• The entire box is white and and illegible
  https://svelte.dev/examples/slot-props

• Blue text is barely legible
  https://svelte.dev/examples/hacker-news

On light mode

• Text color is grey and barely legible
  https://svelte.dev/examples/bar-chart

• The graph's lines aren't visible
  https://svelte.dev/examples/scatterplot

• Grey text is too light
  https://svelte.dev/examples/hacker-news

[dummdidumm]

hackernews, scatterplot and component-bindings should be better now.