Sidebar Layout Builder

Create sidebar layouts with collapsible panels, widget slots, and content area ratios.

Tested tool guide Tested browser tools Checked August 16, 2026

What Sidebar Layout Builder does and how it behaves

The Sidebar Layout Builder assembles the classic sidebar-and-content structure used in dashboards, admin panels, and documentation sites. You set the proportions - how much of the container the sidebar claims and what remains for the content - then stack collapsible panels and widget slots into the sidebar, and get a preview plus markup you can take into a project. The surprise most people hit: the sidebar width is a ratio of the container, not a fixed size. That ratio behaves well at desktop widths but leaves almost no room for navigation at phone widths, so plan a breakpoint where the sidebar collapses to a drawer or stacks above the content.

How the result is produced

Ratio and remainder

The sidebar width is entered as a fraction of the container - a quarter, a third, a percentage. The content area always takes the remainder, so the columns sum to the full width; change one ratio and the other recomputes. Because the ratio is relative, a 25% sidebar is 300px in a 1200px container but only about 94px at 375px - fine on desktop, nearly useless on a phone.

Panels, collapse, and widget slots

Panels stack vertically inside the sidebar, each with an expanded and a collapsed state. Collapsing a panel frees vertical space for the others; collapsing the whole sidebar, usually to an icon rail, frees horizontal space. Widget slots are placeholder regions sized for the widgets they will hold. A slot with nothing dropped into it still occupies its space, so empty slots show up as blank gaps rather than disappearing.

Good uses

Sketching a dashboard skeleton before writing the real app: settle the sidebar-to-content proportions and decide where widgets such as a stats card or recent-activity feed sit, so the implementation starts from an agreed layout.
Designing a documentation site or knowledge base whose sidebar holds collapsible navigation sections while the article text keeps the remaining column.
Comparing ratios side by side - a 20% sidebar against a 30% one - to see how much reading width the content area keeps before committing.

Limits and checks

Ratios measure the container, not the viewport. If the container is itself fluid, the sidebar's absolute width drifts with the window size, and the ratio alone does not guarantee a minimum readable width for navigation items.
It is easy to confuse a collapsed panel with a collapsed sidebar: one changes vertical space inside the column, the other changes horizontal space for the whole layout. They are separate controls in the builder, and toggling one does not toggle the other.
The preview shows the layout at the container width you chose, and nothing about a percentage ratio guarantees behavior at other widths. A 30% sidebar is about 112px at 375px wide, so a layout that looks right in the builder can break at narrow viewports unless a breakpoint stacks the sidebar or turns it into a drawer.

Common questions

If I collapse the sidebar, does the content area grow?

No. The ratio fixes the column split, and collapsing the sidebar - or a single panel - only reclaims space inside the sidebar itself; the freed area stays empty rather than feeding the content column. If you want the content to widen when the sidebar closes, the layout needs a separate collapsed-state width, not just the collapse action.

Does the generated layout come with responsive breakpoints for phones?

Only if the generated output includes them - check what it contains before relying on it. A 25% sidebar at phone width leaves roughly 94px for navigation, so unless the output stacks the sidebar above the content or turns it into a drawer below a breakpoint you set, the mobile behavior is your responsibility.

References and verification

The behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.