Implement CSS optimization pipeline with PurgeCSS, Autoprefixer, and cssnano; reduce bundle size by 42% (uncompressed) and 39% (gzipped). Add analysis tool for CSS metrics and update build scripts in package.json. Create comprehensive documentation for CSS optimization process.

postcss.config.cjs

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+/**
+ * PostCSS Configuration
+ * 
+ * Processes compiled Sass output through:
+ * 1. PurgeCSS - Removes unused CSS selectors
+ * 2. Autoprefixer - Adds vendor prefixes for browser compatibility
+ * 3. cssnano - Minifies and optimizes CSS (production only)
+ */
+
+const purgecss = require('@fullhuman/postcss-purgecss').default;
+const autoprefixer = require('autoprefixer');
+const cssnano = require('cssnano');
+
+const isProduction = process.env.NODE_ENV === 'production';
+
+module.exports = {
+  plugins: [
+    // Only run PurgeCSS in production or when explicitly enabled
+    ...(isProduction || process.env.PURGECSS === 'true'
+      ? [
+          purgecss({
+            // Scan all content files for class names
+            content: [
+              './**/*.tsx',
+              './**/*.ts',
+              './**/*.md',
+              './**/*.yaml',
+              './**/*.html',
+              './static/js/**/*.js',
+              './static/vendor/**/*.js',
+              // Ignore node_modules except for specific libraries that inject classes
+              '!./node_modules/**/*',
+            ],
+            
+            // Default extractor - looks for class names in content
+            defaultExtractor: content => {
+              // Match all words, including those with dashes and numbers
+              const broadMatches = content.match(/[^<>"'`\s]*[^<>"'`\s:]/g) || [];
+              // Match class names in className="..." or class="..." 
+              const classMatches = content.match(/(?:class|className)=["']([^"']*)["']/g) || [];
+              const classes = classMatches.flatMap(match => {
+                const m = match.match(/["']([^"']*)["']/);
+                return m ? m[1].split(/\s+/) : [];
+              });
+              return [...broadMatches, ...classes];
+            },
+
+            // Safelist - classes that should never be removed
+            // BE VERY CONSERVATIVE - only add classes that are truly dynamic
+            safelist: {
+              // Standard safelist - only truly dynamic state classes
+              standard: [
+                'html',
+                'body',
+                'light',
+                'dark',
+                'show',
+                'hide',
+                'active',
+                'disabled',
+                'open',
+                'collapsed',
+                'collapsing',
+              ],
+              
+              // Deep safelist - MINIMAL - only truly dynamic components
+              deep: [
+                // Bootstrap JS components (only if actually used with JS)
+                /dropdown-menu/,
+                /dropdown-item/,
+                /modal-backdrop/,
+                /fade/,
+                
+                // Third-party libraries
+                /cm-/,
+                /CodeMirror/,
+                /lottie/,
+              ],
+
+              // Greedy safelist - VERY MINIMAL
+              greedy: [
+                /data-theme/, // Theme switching
+              ],
+            },
+
+            // Reject specific patterns - don't remove these even if not found
+            rejected: [],
+            
+            // Variables - keep CSS custom properties
+            variables: true,
+            
+            // Keyframes - keep animation keyframes
+            keyframes: true,
+            
+            // Font-face rules
+            fontFace: true,
+          }),
+        ]
+      : []),
+
+    // Autoprefixer - adds vendor prefixes
+    autoprefixer({
+      overrideBrowserslist: [
+        '>0.2%',
+        'not dead',
+        'not op_mini all',
+        'last 2 versions',
+      ],
+    }),
+
+    // cssnano - minification (production only)
+    ...(isProduction
+      ? [
+          cssnano({
+            preset: [
+              'default',
+              {
+                discardComments: {
+                  removeAll: true,
+                },
+                normalizeWhitespace: true,
+                colormin: true,
+                minifySelectors: true,
+              },
+            ],
+          }),
+        ]
+      : []),
+  ],
+};
+