added log in button to unauthenticated courseware

lms/static/sass/course/layout/_courseware_header.scss

@@ -67,7 +67,39 @@ header.global.slim {
   @include linear-gradient(top, #fff, #eee);
 
   .guest .secondary {
+    margin-right: 0;
+  }
+
+  .guest .secondary a {
     display: none;
+
+    &#login {
+      display: block;
+      @include background-image(linear-gradient(-90deg, lighten($blue, 8%), lighten($blue, 5%) 50%, $blue 50%, darken($blue, 10%) 100%));
+      border: 1px solid transparent;
+      border-color: darken($blue, 10%);
+      @include border-radius(3px);
+      @include box-sizing(border-box);
+      @include box-shadow(0 1px 0 0 rgba(255,255,255, 0.6));
+      color: #fff;
+      display: inline-block;
+      font-family: $sans-serif;
+      font-size: 14px;
+      font-weight: bold;
+      @include inline-block;
+      letter-spacing: 0;
+      line-height: 1em;
+      margin: 4px;
+      padding: 6px 12px 8px;
+      text-decoration: none;
+      text-transform: none;
+      text-shadow: 0 -1px rgba(0, 0, 0, 0.6);
+      vertical-align: middle;
+
+      &:hover, &.active {
+        @include background-image(linear-gradient(-90deg, $blue, $blue 50%, $blue 50%, $blue 100%));
+      }
+    }
   }
 
   nav {
@@ -129,7 +161,7 @@ header.global.slim {
 
   a#signup {
     position: relative;
-    margin-top: 4px;
+    margin-top: 3px;
     padding: 6px 12px 8px;
     text-transform: none;
     font-size: 14px;