diff --git a/web_src/css/modules/tippy.css b/web_src/css/modules/tippy.css
index 53c3d5aaeac6e..b62f906870213 100644
--- a/web_src/css/modules/tippy.css
+++ b/web_src/css/modules/tippy.css
@@ -28,6 +28,14 @@
   z-index: 1;
 }
 
+/* for vue3-calendar-heatmap's tippy instances */
+.tippy-box:not([data-theme]) {
+  padding: 0.5rem 1rem;
+  background-color: var(--color-tooltip-bg);
+  color: var(--color-tooltip-text);
+  border: none;
+}
+
 /* bare theme, no styling at all, except box-shadow */
 .tippy-box[data-theme="bare"] {
   border: none;