fix styling for table filters th border

src/components/runners/RunnersOverview.svelte

@@ -73,7 +73,7 @@
       <table>
         <thead>
           <tr>
-            <th>
+            <th style="border-bottom: 1px solid #ddd;">
               <input
                 type="checkbox"
                 class="focus:ring-indigo-500 h-4 w-4 text-indigo-600 border-gray-300 rounded"
@@ -91,19 +91,19 @@
             <Th {handler} orderBy="firstname">First Name</Th>
             <Th {handler} orderBy="middlename">Middle Name</Th>
             <Th {handler} orderBy="lastname">Last Name</Th>
-            <th>Gruppe</th>
+            <th style="border-bottom: 1px solid #ddd;">Gruppe</th>
             <Th {handler} orderBy="distance">Distanz</Th>
-            <th>{$_("action")}</th>
+            <th style="border-bottom: 1px solid #ddd;">{$_("action")}</th>
           </tr>
           <tr>
-            <th />
+            <th style="border-bottom: 1px solid #ddd;" />
             <ThFilter {handler} filterBy="id" />
             <ThFilter {handler} filterBy="firstname" />
             <ThFilter {handler} filterBy="middlename" />
             <ThFilter {handler} filterBy="lastname" />
             <ThFilterGroup groups={selectgroups} {handler} />
-            <th />
-            <th />
+            <th style="border-bottom: 1px solid #ddd;" />
+            <th style="border-bottom: 1px solid #ddd;" />
           </tr>
         </thead>
         <tbody>