consistent button styling

(black text on blue for primary for now to hit contrast needs)
Also re-enable underlines for hover on links.
At some point this needs a thorough review for accessibility

src/styles/_dark.scss

@@ -6,13 +6,10 @@ html.dark {
   body {
     $blue: $blue;
     color: darken($light, 10%) !important;
-    a {
+    a:not(.btn) {
       color: lighten($blue, 10%);
     }
-    a.btn {
-      color: $light !important;
-    }
-    a:hover {
+    a:not(.btn):hover {
       color: lighten($blue, 35%);
     }
     .active:hover {

src/styles/_overrides.scss

@@ -68,7 +68,7 @@ a code {
 .version-dropdown.dropdown-menu,
 [aria-labelledby="page-actions-button"] {
   border-radius: $border-radius !important;
-  border-top-color: #4d89b1 !important;
+  border-top-color: $blue !important;
 }
 
 .dropdown-item.active,

src/styles/_theme.scss

@@ -47,7 +47,7 @@ $h6-font-size: $font-size-base * 0.8;
 $text-muted: $gray-500;
 $code-color: #457a00;
 $link-decoration: none;
-$link-hover-decoration: none;
+$link-hover-decoration: underline;
 
 // forms
 $input-btn-padding-y: 0.5rem;