Block themes follow modern web development best practices by default, solving the render-blocking and unused CSS problems that plague classic themes. Understanding the three types of CSS helps explain how this works.
External CSS (separate .css files) blocks page rendering while downloading and parsing. Internal CSS (style blocks in HTML) avoids render blocking. Inline CSS (style attributes) targets specific elements for customization.
Block themes intelligently load only the CSS needed for blocks actually present on each page. Small stylesheets get inlined automatically to avoid render blocking, while larger ones remain external only when necessary.
The result? No unused CSS and minimal render blocking resources. When you see lots of inline styles in a block theme, it usually means poor design system implementation – you should be using global styles that cascade naturally rather than styling every individual element.