diff --git a/apps/dashboard/src/app/(dashboard)/deployments/components/ProjectFilter.tsx b/apps/dashboard/src/app/(dashboard)/deployments/components/ProjectFilter.tsx
index 6e38253c8..be7eb2e47 100644
--- a/apps/dashboard/src/app/(dashboard)/deployments/components/ProjectFilter.tsx
+++ b/apps/dashboard/src/app/(dashboard)/deployments/components/ProjectFilter.tsx
@@ -51,7 +51,7 @@ export const ProjectFilter: React.FC<ProjectFilterProps> = ({
       </button>
 
       {isOpen && (
-        <div className="absolute top-full start-0 z-50 mt-2 max-h-96 w-72 overflow-y-auto rounded-xl border border-border/50 bg-popover overflow-hidden">
+        <div className="absolute top-full start-0 z-50 mt-2 max-h-96 w-72 overflow-y-auto rounded-xl border border-border/50 bg-popover">
           {/* All Projects Option */}
           <button
             onClick={() => {
diff --git a/apps/dashboard/src/components/ui/CustomSelect.tsx b/apps/dashboard/src/components/ui/CustomSelect.tsx
index 37104d77e..8ffe16ae0 100644
--- a/apps/dashboard/src/components/ui/CustomSelect.tsx
+++ b/apps/dashboard/src/components/ui/CustomSelect.tsx
@@ -161,7 +161,7 @@ export function CustomSelect<T extends string>({
         <div
           ref={menuRef}
           role="listbox"
-          className="fixed z-[10050] overflow-hidden rounded-2xl border border-border/50 bg-popover shadow-xl shadow-black/[0.08]"
+          className="fixed z-[10050] flex flex-col overflow-hidden rounded-2xl border border-border/50 bg-popover shadow-xl shadow-black/[0.08]"
           style={{
             left: menuPosition.left,
             width: menuPosition.width,
@@ -171,7 +171,7 @@ export function CustomSelect<T extends string>({
               : { bottom: menuPosition.bottom }),
           }}
         >
-          <div className="max-h-full overflow-y-auto py-1.5">
+          <div className="min-h-0 flex-1 overflow-y-auto py-1.5">
             {options.map((option) => {
               const isSelected = option.value === value;
               return (
diff --git a/apps/dashboard/src/components/ui/custom-select.render.test.tsx b/apps/dashboard/src/components/ui/custom-select.render.test.tsx
new file mode 100644
index 000000000..ce9201bfc
--- /dev/null
+++ b/apps/dashboard/src/components/ui/custom-select.render.test.tsx
@@ -0,0 +1,70 @@
+import { describe, expect, it } from "vitest";
+import { readFileSync } from "node:fs";
+import { resolve } from "node:path";
+import { renderToStaticMarkup } from "react-dom/server";
+import { CustomSelect } from "./CustomSelect";
+
+/**
+ * Regression test for Supabase / database connection dropdown scrolling bug.
+ *
+ * Problem:
+ * When connecting a Supabase database to a project (via "Use in a project" modal),
+ * the target project dropdown menu could not be scrolled when there were many projects.
+ * The portal outer container had `overflow-hidden` and `maxHeight`, but lacked
+ * `flex flex-col`, causing the child `max-h-full` to fail resolving against parent
+ * indefinite height (`height: auto`). The inner container expanded to full content
+ * height, preventing `overflow-y-auto` from activating, while the outer container
+ * clipped the content at `maxHeight` (e.g. 256px).
+ *
+ * Fix:
+ * 1. Outer container has `flex flex-col overflow-hidden` with `maxHeight`.
+ * 2. Inner container has `min-h-0 flex-1 overflow-y-auto` so flexbox constrains
+ *    the inner container to available height and properly activates vertical scrolling.
+ */
+describe("CustomSelect — scrollable dropdown structure", () => {
+  const options = Array.from({ length: 25 }, (_, i) => ({
+    value: `proj-${i + 1}`,
+    label: `Project ${i + 1}`,
+    description: `project-${i + 1}.example.com`,
+  }));
+
+  it("renders trigger button with placeholder when unselected", () => {
+    const html = renderToStaticMarkup(
+      <CustomSelect
+        value=""
+        options={options}
+        onChange={() => {}}
+        placeholder="Select a project…"
+      />,
+    );
+
+    expect(html).toContain("Select a project…");
+    expect(html).toContain('aria-haspopup="listbox"');
+    expect(html).toContain('aria-expanded="false"');
+  });
+
+  it("renders selected option label and description when value matches", () => {
+    const html = renderToStaticMarkup(
+      <CustomSelect
+        value="proj-3"
+        options={options}
+        onChange={() => {}}
+        placeholder="Select a project…"
+      />,
+    );
+
+    expect(html).toContain("Project 3");
+    expect(html).toContain("project-3.example.com");
+  });
+
+  it("ensures CustomSelect source code uses flex-col on outer menu and min-h-0 flex-1 overflow-y-auto on inner list", () => {
+    const sourcePath = resolve(__dirname, "CustomSelect.tsx");
+    const source = readFileSync(sourcePath, "utf-8");
+
+    // Outer portal container must be flex flex-col to bound children in flex layout
+    expect(source).toMatch(/className="[^"]*flex flex-col overflow-hidden[^"]*bg-popover/);
+
+    // Inner options list must have min-h-0 flex-1 overflow-y-auto to scroll when content exceeds max-height
+    expect(source).toMatch(/className="[^"]*min-h-0 flex-1 overflow-y-auto[^"]*"/);
+  });
+});