diff --git a/booklore-ui/src/app/features/stats/component/user-stats/charts/reading-session-heatmap/reading-session-heatmap.component.ts b/booklore-ui/src/app/features/stats/component/user-stats/charts/reading-session-heatmap/reading-session-heatmap.component.ts
index 4a6d4aa97..46e8db186 100644
--- a/booklore-ui/src/app/features/stats/component/user-stats/charts/reading-session-heatmap/reading-session-heatmap.component.ts
+++ b/booklore-ui/src/app/features/stats/component/user-stats/charts/reading-session-heatmap/reading-session-heatmap.component.ts
@@ -178,7 +178,10 @@ export class ReadingSessionHeatmapComponent implements OnInit, OnDestroy {
 
     while (currentDate <= endDate || weekIndex === 0) {
       for (let dayOfWeek = 0; dayOfWeek < 7; dayOfWeek++) {
-        const dateStr = currentDate.toISOString().split('T')[0];
+        const year = currentDate.getFullYear();
+        const month = String(currentDate.getMonth() + 1).padStart(2, '0');
+        const day = String(currentDate.getDate()).padStart(2, '0');
+        const dateStr = `${year}-${month}-${day}`;
 
         if (currentDate >= startDate && currentDate <= endDate) {
           const count = sessionMap.get(dateStr) || 0;
diff --git a/booklore-ui/src/app/features/stats/component/user-stats/charts/reading-session-timeline/reading-session-timeline.component.html b/booklore-ui/src/app/features/stats/component/user-stats/charts/reading-session-timeline/reading-session-timeline.component.html
index fce032e68..68ef18863 100644
--- a/booklore-ui/src/app/features/stats/component/user-stats/charts/reading-session-timeline/reading-session-timeline.component.html
+++ b/booklore-ui/src/app/features/stats/component/user-stats/charts/reading-session-timeline/reading-session-timeline.component.html
@@ -81,6 +81,7 @@
                      [pTooltip]="getTooltipContent(session)"
                      [escape]="false"
                      tooltipPosition="top"
+                     tooltipStyleClass="session-timeline-tooltip"
                      [appendTo]="'body'">
                   @if (isDurationGreaterThanOneHour(session.duration)) {
                     <div class="session-content">
diff --git a/booklore-ui/src/app/features/stats/component/user-stats/charts/reading-session-timeline/reading-session-timeline.component.scss b/booklore-ui/src/app/features/stats/component/user-stats/charts/reading-session-timeline/reading-session-timeline.component.scss
index 375a6c7fb..232d22ce8 100644
--- a/booklore-ui/src/app/features/stats/component/user-stats/charts/reading-session-timeline/reading-session-timeline.component.scss
+++ b/booklore-ui/src/app/features/stats/component/user-stats/charts/reading-session-timeline/reading-session-timeline.component.scss
@@ -367,7 +367,7 @@
   }
 }
 
-::ng-deep .p-tooltip {
+::ng-deep .session-timeline-tooltip.p-tooltip {
   --p-tooltip-max-width: 300px;
   --p-tooltip-background: rgba(30, 30, 30, 0.98);
   --p-tooltip-color: #ffffff;