[Glitch] Improve style of web UI account tabs

Port of 38b9af76a2 to glitch

app/javascript/flavours/glitch/styles/components/accounts.scss

@@ -431,22 +431,24 @@
 }
 
 .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 {
@@ -460,7 +462,7 @@
         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 {