auto merge of #7184 : smvv/rust/doc_css, r=brson

After reading issue #7077, all header elements had a border. In my opinion those borders are a bit too much distraction. I tried a different approach with increasing the padding and font size, and omitting the borders.

Comparison:
http://smvv.io/rust-doc/std/hashmap.html
http://static.rust-lang.org/doc/std/hashmap.html

Note: the highlighted code blocks are not caused by this commit.

I left the border of the code block / function signature as is. The reason behind that is that code blocks are really block elements, while headers are not. What do you guys think?

doc/rust.css

@@ -12,41 +12,38 @@ body {
 }
 
 h1 {
-    font-size: 20pt;
-    margin-top: 2em;
+    font-size: 24pt;
+    margin-top: 1.6em;
     padding-left: 0.4em;
     line-height: 1.6em;
     background-color:#FFF2CE;
     border-radius: 0.2em;
-    border: 1px solid rgba(0, 0, 0, 0.15);
 }
 
 h2 {
-    font-size: 15pt;
-    margin-top: 2em;
-    padding-left: 0.4em;
+    font-size: 16pt;
+    margin-top: 1.6em;
+    padding: 0.2em 0.5em;
     background-color:#FFF2CE;
     border-radius: 0.4em;
-    border: 1px solid rgba(0, 0, 0, 0.15);
 }
 
 h2 code {
     color: #097334;
-    font-size: 15pt;
+    font-size: 16pt;
 }
 
 h3 {
-    font-size: 13pt;
+    font-size: 14pt;
     color: black;
     background-color:#D9E7FF;
     border-radius: 0.4em;
-    border: 1px solid rgba(0, 0, 0, 0.15);
-    padding: 0 0.4em 0 0.4em;
+    padding: 0.2em 0.5em;
 }
 
 h3 code {
     color: #541800;
-    font-size: 13pt;
+    font-size: 14pt;
     font-style: italic;
 }