Improve style of web UI account tabs (#6589)

app/javascript/styles/mastodon/components.scss

@@ -4631,22 +4631,24 @@ a.status-card {
 }
 
 .account__section-headline {
-  background: lighten($ui-base-color, 2%);
-  border-bottom: 1px solid lighten($ui-base-color, 4%);
+  background: darken($ui-base-color, 4%);
+  border-bottom: 1px solid lighten($ui-base-color, 8%);
   cursor: default;
   display: flex;
 
   a {
     display: block;
-    color: $ui-base-lighter-color;
-    padding: 15px 10px;
+    flex: 1 1 auto;
+    color: $ui-primary-color;
+    padding: 15px 0;
     font-size: 14px;
     font-weight: 500;
+    text-align: center;
     text-decoration: none;
     position: relative;
 
     &.active {
-      color: $ui-highlight-color;
+      color: $ui-secondary-color;
 
       &::before,
       &::after {
@@ -4660,7 +4662,7 @@ a.status-card {
         transform: translateX(-50%);
         border-style: solid;
         border-width: 0 10px 10px;
-        border-color: transparent transparent lighten($ui-base-color, 4%);
+        border-color: transparent transparent lighten($ui-base-color, 8%);
       }
 
       &::after {