Fluid layout lets you align elements so that they automatically adjust their alignment and proportions for different page sizes and orientations. You can create a fluid layout by setting sizes and positions in percentages rather than pixels. Responsive documents especially benefit from fluid layout.
Fluid layout can also work with fixed-size elements.
To use percentages instead of pixels, click px in the field in the Properties panel, and select % from the dropdown.
To convert all the position and size values to percentages, click the Use percentages button.
You can use a mix of percentage-based and pixel-based values in your document.
Alignment and distribution tools
When the Selection tool is active, you can use the alignment and distribution tools in the tool options bar at the top in order to position elements. Enable the Fluid layout option (which requires the Align to container option to be enabled first) to use percentages.