change Ukraine banner to SvelteHack banner

[karimfromjordan]

This PR changes the Ukraine banner to a SvelteHack banner

• I removed some duplicated CSS that was there
• renamed all ukr CSS classes and custom props to just banner
• added three CSS custom props to make it easier to change the banner

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Name	Status	Preview	Comments	Updated
hn	✅ Ready (Inspect)	Visit Preview	💬 Add your feedback	Feb 20, 2023 at 4:32AM (UTC)
svelte-dev	✅ Ready (Inspect)	Visit Preview	💬 Add your feedback	Feb 20, 2023 at 4:32AM (UTC)

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