CSS: fix some border color regressions

tildes/scss/_base.scss

@@ -8,6 +8,10 @@ html {
   font-size: $html-font-size;
 }
 
+* {
+  border-color: var(--border-color);
+}
+
 a {
   text-decoration: none;
 
@@ -282,10 +286,10 @@ tbody tr:nth-of-type(2n + 1) {
 
 td,
 th {
-  border: $border-width solid;
+  border: $border-width solid var(--border-color);
   padding: $unit-3 $unit-2;
 }
 
 th {
-  border-bottom-width: $border-width-lg;
+  border-bottom: $border-width-lg solid var(--foreground-highlight-color);
 }

tildes/scss/modules/_comment.scss

@@ -2,8 +2,7 @@
 // SPDX-License-Identifier: AGPL-3.0-or-later
 
 .comment {
-  border-left: 1px solid;
-  border-color: inherit;
+  border-left: 1px solid var(--border-color);
   margin-bottom: 0.4rem;
 
   &:target > .comment-itself {
@@ -12,8 +11,7 @@
 }
 
 .comment[data-comment-depth="0"] {
-  border-bottom: 1px solid;
-  border-color: inherit;
+  border-bottom: 1px solid var(--border-color);
 }
 
 .comment-header {