changed dockerfile back button to look nicer

Signed-off-by: Nathan Hsieh <hsieh.nathan@gmail.com>

docs/sources/userguide/level1.md

@@ -2,7 +2,7 @@ page_title: Docker Images Test
 page_description: How to work with Docker images.
 page_keywords: documentation, docs, the docker guide, docker guide, docker, docker platform, virtualization framework, docker.io, Docker images, Docker image, image management, Docker repos, Docker repositories, docker, docker tag, docker tags, Docker Hub, collaboration
 
-<a title="back" class="btn btn-primary back" href="/userguide/dockerimages/#creating-our-own-images">Back</a>
+<a title="back" class="dockerfile back" href="/userguide/dockerimages/#creating-our-own-images">Back</a>
 
 # Dockerfile Tutorial
 

docs/sources/userguide/level2.md

@@ -2,7 +2,7 @@ page_title: Docker Images Test
 page_description: How to work with Docker images.
 page_keywords: documentation, docs, the docker guide, docker guide, docker, docker platform, virtualization framework, docker.io, Docker images, Docker image, image management, Docker repos, Docker repositories, docker, docker tag, docker tags, Docker Hub, collaboration
 
-<a title="back" class="btn btn-primary back" href="/userguide/dockerimages/#creating-our-own-images">Back</a>
+<a title="back" class="dockerfile back" href="/userguide/dockerimages/#creating-our-own-images">Back</a>
 
 #Dockerfile Tutorial
 

docs/theme/mkdocs/css/dockerfile_tutorial.css

@@ -56,4 +56,8 @@ div.level_error {
     width: 90px;
     margin-right: 0;
     padding: 0 0 2px 0;
+}
+.dockerfile.back {
+    display: block;
+    margin-top: 5px;
 }