fix(input-date-picker, date-picker): ensure day selection doesn't activate the previous day in certain scenarios

packages/calcite-components/src/components/date-picker/date-picker.e2e.ts

@@ -565,6 +565,22 @@ describe("calcite-date-picker", () => {
     await page.waitForChanges();
     expect(await datePicker.getProperty("value")).toEqual(["2020-09-15", "2020-09-30"]);
   });
+
+  it("doesn't select the previous day in CEST timezone", async () => {
+    const page = await newE2EPage();
+    await page.emulateTimezone("Europe/Zurich");
+
+    await page.setContent(html` <calcite-date-picker value="1850-03-12"></calcite-date-picker> `);
+
+    const datePicker = await page.find("calcite-date-picker");
+
+    expect(await datePicker.getProperty("value")).toBe("1850-03-12");
+
+    await selectDay("18500307", page, "mouse");
+    await page.waitForChanges();
+
+    expect(await datePicker.getProperty("value")).toBe("1850-03-07");
+  });
 });
 
 async function setActiveDate(page: E2EPage, date: string): Promise<void> {

packages/calcite-components/src/utils/date.ts

@@ -151,7 +151,10 @@ export function datePartsFromLocalizedString(
  */
 export function dateToISO(date?: Date): string {
   if (date instanceof Date) {
-    return new Date(date.getTime() - date.getTimezoneOffset() * 60000).toISOString().split("T")[0];
+    const month = String(date.getMonth() + 1).padStart(2, "0");
+    const day = String(date.getDate()).padStart(2, "0");
+    const year = String(date.getFullYear()).padStart(4, "0");
+    return `${year}-${month}-${day}`;
   }
   return "";
 }