# Theme System Performance Audit **Date:** 2026-03-21 **Agent:** performance-optimizer **Scope:** Dark/light theme implementation across `ThemeToggle.astro`, `BaseLayout.astro`, `design-tokens.css`, `global.css` --- ## Executive Summary The theme system is **well-implemented from a performance standpoint**. FOUC is eliminated, CSS transitions are scoped, and JS is minimal. A few targeted improvements can reduce reflow cost and eliminate a minor memory leak risk. | Area | Status | Score | |------|--------|-------| | FOUC prevention (init script) | ✅ Correct | A | | CSS custom property strategy | ✅ Efficient | A | | Theme toggle JS footprint | ⚠️ Minor issues | B+ | | CLS during theme switch | ✅ Low risk | A | | Paint / reflow cost | ⚠️ Improvable | B | | Memory leak risk | ⚠️ Present | B | | Reduced-motion support | ✅ Correct | A | --- ## 1. Theme Initialization Script (FOUC Prevention) **File:** `BaseLayout.astro` — lines 208–224 ```js (function() { try { var stored = localStorage.getItem('theme'); var prefersDark = window.matchMedia('(prefers-color-scheme: dark)').matches; var isDark = stored === 'dark' || (!stored && prefersDark); if (isDark) document.documentElement.classList.add('dark'); if (stored) { var metas = document.querySelectorAll('meta[name="theme-color"]'); var color = isDark ? '#0f172a' : '#0891b2'; metas.forEach(function(m) { m.setAttribute('content', color); }); } } catch(e) {} })(); ``` ### Analysis **Timing:** The script is `is:inline` and placed in `` before any `