feat: add variable to config HomePage width (close #2055)

[haoranpb]

Summary

Fix: #2055

It took me a while to realize that palette.styl can do more than only color. The naming seems to be out-dated?

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• Code style update
• Refactor
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If changing the UI of default theme, please provide the before/after screenshot:

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• No

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The PR fulfills these requirements:

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To avoid wasting your time, it's best to open a feature request issue first and wait for approval before working on it.

Other information:

[billyyyyy3320]

It should be discuss whether to rename palette.styl.