prefer CSS custom properties

Use CSS custom properties (CSS variables) instead of hardcoded values for fonts, spacing, colors, and other design tokens. This improves maintainability, enables consistent theming, and makes design system changes easier to implement across the codebase.

Examples of preferred patterns:

/* Good - uses custom properties */
font-family: var(--font-family);
margin-bottom: var(--space-2);
border: 1px solid var(--content-border-color);

/* Avoid - hardcoded values */
font-family: system-ui, Arial, sans-serif;
margin-bottom: 10px;
border: 1px solid var(--primary-low);

When choosing custom properties, use semantic names that reflect the property’s purpose (like --content-border-color for content separation vs --input-border-color for form inputs) rather than generic color names.