CSS Positioning Fundamentals
Understanding CSS positioning is crucial for debugging layout issues, especially when elements appear in unexpected locations.
Position Values:
- static (default): Normal document flow, ignores top/left/z-index
- relative: Offset from normal position, creates stacking context
- absolute: Positioned relative to nearest positioned ancestor
- fixed: Positioned relative to viewport
- sticky: Switches between relative and fixed based on scroll
First Principle: Positioned elements are removed from normal document flow (except relative and sticky in some cases).
Common Issues:
- Absolute positioning without positioned parent: Elements position relative to
<html> - Z-index not working: Element needs
position≠ static - Sticky not working: Container height must be larger than sticky element
Debugging Questions:
- What is the containing block? (nearest positioned ancestor)
- Is there a stacking context involved?
- Are offset values (top/left/right/bottom) specified?
Mental Model: Think of positioning like layers of transparency sheets - static is the base layer, positioned elements float above.
Best Practice: Use position: relative on containers when children need position: absolute.
Related: CSS Stacking Context, CSS Layout Debugging Strategy