syncs styling rules for buttons/inputs to ensure consistency

cms/static/sass/_base.scss

@@ -14,7 +14,7 @@ body {
   color: $gray-d2;
 }
 
-body, input {
+body, input, button {
   font-family: 'Open Sans', sans-serif;
 }
 

common/lib/xmodule/xmodule/css/capa/display.scss

@@ -553,7 +553,8 @@ section.problem {
 
     .save, .check, .show {
       height: ($baseline*2);
-      font-weight: 600;
+      font-weight: 500;
+      vertical-align: middle;
     }
 
     .save {
@@ -564,7 +565,7 @@ section.problem {
 
       .show-label {
         font-size: 1.0em;
-        font-weight: 600;
+        font-weight: 500;
       }
     }