Which feature allows you to customize the layout of forms within your application?

The Interface Designer is the correct choice because it provides a comprehensive environment for creating and customizing the layout of forms in Appian applications. Through the Interface Designer, developers can visually design forms by arranging components, configuring properties, and defining interactions.

This tool enables users to drag and drop elements, set up logical arrangements, and ensure that the overall user experience is tailored to meet the specific needs of an application. It also supports the integration of various user interface components, making it a powerful feature for creating smooth and visually appealing forms.

Other options, while they offer some level of customization, do not serve the primary function of customizing form layouts in the same way. For instance, CSS Customization allows for styling adjustments but does not provide the necessary framework or tools for layout configuration in a visual format. Tab Layouts are useful for organizing content within forms but are not designed for comprehensive layout alterations. Record Views focus on displaying and managing data but do not directly pertain to form layout customization. Thus, the Interface Designer stands out as the dedicated tool for this specific purpose.