fix small style things that Justine ponted out

app/styles/app/_mixins/vars.sass

@@ -1,5 +1,6 @@
 
 $font-size-m: 16px
+$font-size-sm: 14px
 $line-height-m: 1.3
 
 // colors

app/styles/app/layouts/buildheader.sass

@@ -14,8 +14,10 @@
   margin: 0
   font-weight: 400
   font-size: 35px
-  a:hover
-    text-decoration: underline
+  a
+    color: $grey3
+    &:hover
+      text-decoration: underline
 
 .repo-header-icons
   line-height: 1

app/styles/app/modules/tabs.sass

@@ -1,6 +1,7 @@
 
 .tabnav
   color: $grey2
+  font-size: $font-size-sm
   ul
     @include resetul
     width: 100%
@@ -24,7 +25,7 @@
       content: ""
       position: absolute
       left: 0
-      bottom: -3px
+      bottom: -0.25em
       width: 100%
       height: 2px
       background-color: $teal2