diff --git a/src/Index.tsx b/src/Index.tsx
index 34b515e..56f52ad 100644
--- a/src/Index.tsx
+++ b/src/Index.tsx
@@ -1,7 +1,10 @@
-import { useEffect, useState } from "react";
 import ShapeCanvas from "@/components/canvas/ShapeCanvas";
+import PresetSelector from "@/components/controls/PresetSelector";
+import { Slider } from "@/components/ui/slider";
 import { useShapeState } from "@/hooks/useShapeState";
+import { useEffect, useState } from "react";
 import Layout from "./Layout";
+import { cn } from "./lib/utils";
 
 function Index() {
     const [dimensions, setDimensions] = useState({
@@ -26,8 +29,34 @@ function Index() {
 
     const [state, setState] = useShapeState(centerX, centerY);
 
+    const sidebarContent = (
+        <div className="flex flex-col gap-4">
+            <div className="flex flex-col gap-2">
+                <span className="text-sm font-medium">Shape</span>
+                <PresetSelector value={state.preset} onChange={(preset) => setState({ ...state, preset })} />
+            </div>
+            <div className="flex flex-col gap-2">
+                <span
+                    className={cn(
+                        "text-sm font-medium",
+                        state.preset === "circle" ? "opacity-50 pointer-events-none select-none" : "",
+                    )}
+                >
+                    Roundness
+                </span>
+                <Slider
+                    value={[state.roundness]}
+                    min={0}
+                    max={100}
+                    onValueChange={([v]) => setState({ ...state, roundness: v })}
+                    className={state.preset === "circle" ? "opacity-50 pointer-events-none" : ""}
+                />
+            </div>
+        </div>
+    );
+
     return (
-        <Layout sidebarContent={<>controls here</>}>
+        <Layout sidebarContent={sidebarContent}>
             <ShapeCanvas state={state} onStateChange={setState} />
         </Layout>
     );
diff --git a/src/components/controls/PresetSelector.tsx b/src/components/controls/PresetSelector.tsx
new file mode 100644
index 0000000..eb5f689
--- /dev/null
+++ b/src/components/controls/PresetSelector.tsx
@@ -0,0 +1,31 @@
+import { Button } from "@/components/ui/button";
+import type { Preset } from "@/types/shape";
+
+const presets: { value: Preset; label: string }[] = [
+    { value: "triangle", label: "Triangle" },
+    { value: "square", label: "Square" },
+    { value: "circle", label: "Circle" },
+];
+
+export default function PresetSelector({
+    value,
+    onChange,
+}: {
+    value: Preset;
+    onChange: (preset: Preset) => void;
+}) {
+    return (
+        <div className="flex gap-2">
+            {presets.map((preset) => (
+                <Button
+                    key={preset.value}
+                    variant={value === preset.value ? "default" : "outline"}
+                    size="sm"
+                    onClick={() => onChange(preset.value)}
+                >
+                    {preset.label}
+                </Button>
+            ))}
+        </div>
+    );
+}
diff --git a/src/components/ui/button.tsx b/src/components/ui/button.tsx
index 846eda8..a881f32 100644
--- a/src/components/ui/button.tsx
+++ b/src/components/ui/button.tsx
@@ -9,7 +9,7 @@ const buttonVariants = cva(
     {
         variants: {
             variant: {
-                default: "bg-primary text-primary-foreground hover:bg-primary/90",
+                default: "bg-primary text-primary-foreground hover:bg-primary/90 border border-primary",
                 destructive:
                     "bg-destructive text-white hover:bg-destructive/90 focus-visible:ring-destructive/20 dark:focus-visible:ring-destructive/40 dark:bg-destructive/60",
                 outline: