Topic
Definition
CSS positioning selects how an element participates in layout via position values (static, relative, absolute, fixed, sticky) and how overlapping boxes paint via stacking contexts and z-index.
In simpler words
static is normal flow. relative nudges without leaving the flow. absolute and fixed remove the element from flow and place it against a containing block. sticky sticks while scrolling. z-index only works on positioned (or flex/grid) items in a stacking context.
Position modes, containing blocks, offsets, stacking, and when absolute is the wrong tool for page layout.
Position modes, containing blocks, offsets, stacking, and when absolute is the wrong tool for page layout.
Start by identifying which value or browser behavior changes. Then describe the UI from that current input instead of editing the DOM as a separate source of truth.
.card {
position: relative;
}
.card .badge {
position: absolute;
top: 8px;
right: 8px;
}
.site-header {
position: sticky;
top: 0;
z-index: 10;
}Read the example from data and control flow to the resulting UI. Keep the component boundary small.
Keep rendering as a calculation. Put user-triggered changes in event handlers, preserve UI memory in state, and reserve external synchronization for Effects or the server-state layer.
Name values by their UI meaning, test the loading and error path when data is remote, and avoid keeping two editable copies of the same value.
Ask before adding code: is this local UI memory, shared client state, or Nest-owned server state?
Definition
High-bug areas are places where a small API misuse looks correct but produces stale UI, duplicate work, or silent failures.
In simpler words
Each mistake below shows Wrong vs Right code — compare them side by side.
When something misbehaves, match the symptom to a pattern below before rewriting the feature.
Prefer fixing the ownership or update path over adding another Effect or sync step.
// Wrong
.page { /* position: static (default) */ }
.badge {
position: absolute;
top: 0;
right: 0;
}
// Right
.page {
position: relative;
}
.badge {
position: absolute;
top: 0;
right: 0;
}Absolute elements position against the nearest positioned ancestor. Without one, they use the initial containing block.
// Wrong
.sidebar { position: absolute; left: 0; width: 240px; }
.main { position: absolute; left: 240px; right: 0; }
// Right
.layout {
display: grid;
grid-template-columns: 240px 1fr;
}Absolute layout fights scrolling, wrapping, and content growth. Use flow, flex, or grid for structure.
// Wrong
.label {
position: static;
z-index: 99;
}
// Right
.label {
position: relative;
z-index: 99;
}z-index applies to positioned elements (and flex/grid items), not ordinary static boxes.
Live playground
Change one input at a time and predict the next render.
No interactive demo for course-css-positioning yet — use the code samples and Wrong vs Right examples above.
Test
At least 10 questions — mix of concept, syntax, practical, and logic. Score ≥ 80% (enforced by the API) to save progress.
Checking your session…
10 questions · concept 3 · syntax 3 · practical 2 · logic 2