Fix more incorrect border colors in default theme

tildes/scss/modules/_message.scss

@@ -4,6 +4,7 @@
 .message {
   margin-bottom: 0.4rem;
   border: 1px solid;
+  border-color: inherit;
 
   header {
     display: flex;

tildes/scss/modules/_settings.scss

@@ -25,5 +25,6 @@
   h2 {
     font-size: 1rem;
     border-bottom: 1px solid;
+    border-color: inherit;
   }
 }

tildes/scss/themes/_theme_base.scss

@@ -86,7 +86,7 @@
     background-color: map-get($theme, "background-secondary");
   }
 
-  th {
+  .table th {
     border-bottom-color: map-get($theme, "foreground-highlight");
   }