[UI] Minor adjustments to styling and classes (#3843)

* Add hint class to Load Average details label

* Remove shadow from table header on flat theme

* Add border to top of table header on /list/server/

web/css/src/themes/flat.css

@@ -57,6 +57,11 @@
 /* Units table
    ========================================================================== */
 
+.units-table-header {
+	box-shadow: none;
+	border-top: 1px solid var(--chart-grid-color);
+}
+
 .units-table-row {
 	@media (--viewport-large) {
 		&:hover {

web/templates/pages/list_services.php

@@ -74,7 +74,7 @@
 					</span>
 				</li>
 				<li class="server-summary-item">
-					<span class="server-summary-list-label"><?= _("Load Average") ?> (1m / 5m / 15m)</span>
+					<span class="server-summary-list-label"><?= _("Load Average") ?> <span class="hint">(1m / 5m / 15m)</span></span>
 					<span class="server-summary-list-value">
 						<?= $sys["sysinfo"]["LOADAVERAGE"] ?>
 					</span>