Freeze the day picker at the top of the page

The day bar moves above everything else and sticks while scrolling, so
switching days never requires scrolling back up. A fixed strip painted
over the safe-area inset keeps content from peeking through above the
stuck bar on notched phones in standalone mode.

src/style.css

@@ -122,15 +122,28 @@ section {
   padding: 16px;
 }
 
-.big-clock {
-  text-align: center;
-  padding: 24px 16px;
+/* Paints over the notch/status-bar strip so content scrolling behind the
+   sticky day bar never peeks through above it. Zero-height where there is no
+   safe-area inset. */
+body::before {
+  content: "";
+  position: fixed;
+  top: 0;
+  left: 0;
+  right: 0;
+  height: env(safe-area-inset-top, 0px);
+  background: var(--bg);
+  z-index: 65;
 }
 
 .day-bar {
+  position: sticky;
+  top: env(safe-area-inset-top, 0px);
+  z-index: 60;
   display: flex;
   gap: 8px;
   align-items: center;
+  flex-wrap: wrap;
   padding: 8px 10px;
 }
 .day-bar input[type="date"] {
@@ -146,6 +159,10 @@ section {
   opacity: 0.4;
   cursor: not-allowed;
 }
+.big-clock {
+  text-align: center;
+  padding: 24px 16px;
+}
 .big-clock .bc-label {
   font-size: 0.8rem;
   text-transform: uppercase;