Three blue rectangles sit in a row on a black-outlined SVG canvas. This example demonstrates interactive CSS transitions on SVG elements using plain React within an HTML page. Each rectangle is assigned a distinct CSS class, and hovering over one gradually changes its fill color and dramatically thickens its stroke over three seconds via the `transition: all 3000ms` rule. The code relies on standard SVG markup and CSS hover pseudo-classes, with no external JavaScript libraries beyond React for structure.