Use * selector for applying theme border colors

This is a lot simpler, and works for almost everything.

tildes/scss/modules/_comment.scss

@@ -12,6 +12,7 @@
 
 .comment[data-comment-depth="0"] {
   border-bottom: 1px solid;
+  border-color: inherit;
 }
 
 .comment-header {

tildes/scss/modules/_input.scss

@@ -1,6 +1,10 @@
 // Copyright (c) 2018 Tildes contributors <code@tildes.net>
 // SPDX-License-Identifier: AGPL-3.0-or-later
 
+.input-group .input-group-addon {
+  border-color: inherit;
+}
+
 .input-invite-code {
   font-size: 0.6rem;
   margin-top: 0.4rem;

tildes/scss/themes/_theme_base.scss

@@ -22,6 +22,10 @@
   // set $is-light as a bool for whether the background seems light or dark
   $is-light: is-color-bright(map-get($theme, "background-primary"));
 
+  * {
+    border-color: map-get($theme, "border");
+  }
+
   a {
     color: map-get($theme, "link");
 
@@ -74,27 +78,6 @@
     background-color: map-get($theme, "background-secondary");
   }
 
-  fieldset {
-    border-color: map-get($theme, "border");
-  }
-
-  figure {
-    border-color: map-get($theme, "border");
-  }
-
-  h1,
-  h2,
-  h3,
-  h4,
-  h5,
-  h6 {
-    border-color: map-get($theme, "border");
-  }
-
-  hr {
-    border-color: map-get($theme, "border");
-  }
-
   main {
     background-color: map-get($theme, "background-primary");
   }
@@ -103,11 +86,6 @@
     background-color: map-get($theme, "background-secondary");
   }
 
-  td,
-  th {
-    border-color: map-get($theme, "border");
-  }
-
   th {
     border-bottom-color: map-get($theme, "foreground-highlight");
   }
@@ -305,14 +283,6 @@
     }
   }
 
-  .comment {
-    border-color: map-get($theme, "border");
-
-    &[data-comment-depth="0"] {
-      border-color: map-get($theme, "border");
-    }
-  }
-
   .comment-header {
     color: map-get($theme, "foreground-highlight");
     background-color: map-get($theme, "background-secondary");
@@ -322,14 +292,10 @@
     border-left-color: map-get($theme, "stripe-target");
   }
 
-  .divider {
-    border-color: map-get($theme, "border");
-
-    &[data-content]::after {
+  .divider[data-content]::after {
     color: map-get($theme, "foreground-primary");
     background-color: map-get($theme, "background-primary");
   }
-  }
 
   .empty-subtitle {
     color: map-get($theme, "foreground-secondary");
@@ -344,10 +310,6 @@
     background-color: map-get($theme, "background-input");
   }
 
-  .form-input:not(:focus) {
-    border-color: map-get($theme, "border");
-  }
-
   // error colors for :invalid inputs, using same approach as Spectre
   .form-input:not(:placeholder-shown):invalid {
     border-color: map-get($theme, "error");
@@ -361,22 +323,13 @@
     }
   }
 
-  .form-markdown-preview {
-    border-color: map-get($theme, "border");
-  }
-
-  .form-select {
-    border-color: map-get($theme, "border");
-
-    &:not([multiple]):not([size]) {
+  .form-select:not([multiple]):not([size]) {
     background-color: map-get($theme, "background-input");
   }
-  }
 
   .input-group-addon {
     background-color: map-get($theme, "background-secondary");
     color: map-get($theme, "foreground-highlight");
-    border-color: map-get($theme, "border");
   }
 
   .label-topic-tag {
@@ -409,8 +362,6 @@
   }
 
   .message {
-    border-color: map-get($theme, "border");
-
     header {
       color: map-get($theme, "foreground-highlight");
       background-color: map-get($theme, "background-secondary");
@@ -463,10 +414,6 @@
     background-color: map-get($theme, "alert");
   }
 
-  .tab {
-    border-color: map-get($theme, "border");
-  }
-
   .tab .tab-item {
     a {
       color: map-get($theme, "foreground-primary");
@@ -506,7 +453,6 @@
 
   .toast {
     color: map-get($theme, "foreground-highlight");
-    border-color: map-get($theme, "border");
     background-color: map-get($theme, "background-secondary");
   }
 
@@ -531,10 +477,6 @@
     }
   }
 
-  .topic {
-    border-color: map-get($theme, "border");
-  }
-
   .topic-listing {
     > li:nth-of-type(2n) {
       color: