Split font css into its own file.

[Randy808]

To run locally, npm install and use the following snippets:

# Bitcoin
export API_URL=https://blockstream.info/api
export PORT=4999
source flavors/blockstream/config.env
source flavors/bitcoin-mainnet/config.env
npm run dev-server

# Liquid
export API_URL=https://blockstream.info/liquid/api
export PORT=5000
source flavors/blockstream/config.env
source flavors/liquid-mainnet/config.env
npm run dev-server

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There should be no visual differences between pages before and after this change.