Hide the spinner buttons in cron dialog, grace time field

static/css/my_checks.css

@@ -145,7 +145,7 @@
 }
 
 #period-slider {
-    margin: 20px 50px 80px 50px;
+    margin: 20px 50px 90px 50px;
 }
 
 #period-slider.noUi-connect {
@@ -177,6 +177,15 @@
     font-weight: bold;
 }
 
+#update-timeout-grace-cron {
+    -moz-appearance: textfield;
+}
+
+#update-timeout-grace-cron::-webkit-outer-spin-button,
+#update-timeout-grace-cron::-webkit-inner-spin-button {
+    -webkit-appearance: none;
+}
+
 .label-tag {
     background-color: var(--tag-bg);
     color: var(--tag-color);