Consider using style-elements

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The issue body is empty, so the first step is to understand what style-elements is and how it could be integrated into the Elm project. Look at the project's current styling approach and dependencies in elm.json. Research the style-elements library documentation and examples to see what changes would be required. Determine if this is a migration or an addition, and assess the scope of changes needed across the codebase.

索引モデルが issue の本文から書いたものです。