embed_gists_on_tumblr.js

// include this in your tumblr theme
$(function() {
  var gist_injectors = $.map($('p.embed_gist').get(), (function(p){
    return function(){
      gist_injectors.shift();
      var gist_id = $(p).find('a:first').attr('href').replace(/.*gist.github.com\//g,'');

      document.write = function(gist_style_link){
        $('head').append(gist_style_link);
        document.write = function(gist_html){
          $(p).replaceWith(gist_html);
          if (gist_injectors[0]) gist_injectors[0]();
        };
      };
      $(document.body).append('<scr'+'ipt src="http://gist.github.com/'+gist_id+'.js"></scr'+'ipt>');
    };
  }));

  if (gist_injectors[0]) gist_injectors[0]();
});

example.html

<!-- embed a gist like this -->
<p class="embed_gist"><a href="http://gist.github.com/234427">http://gist.github.com/234427</a></p>

gist.css

/* I like to add these styles */

.gist {
  line-height: 1.3em !important;
  border: none !important;
  color: white !important;
  margin : 2em !important;
  line-height: 1.5 !important;
  overflow: auto !important;
}

.gist .gist-file {
  border: 0 !important;
  margin-bottom: 1em !important;
}

.gist .gist-file .gist-data {
  background: rgba(0, 0, 0, 0.785156) !important;
  border: none !important;
  padding: 1em !important;
}

.gist .gist-file .gist-meta{
  font-size: 100% !important;
  font-family: "Lucida Grande","Lucida Sans","Lucida Sans Unicode",Geneva,Verdana,sans-serif !important;
  background: transparent !important;
  padding: 0 !important;
}


.gist .gist-syntax .k,
.gist .gist-syntax .kd,
.gist .gist-syntax .kc,
.gist .gist-syntax .o{
  color: orange !important;
}

I am wondering if its possible to turn off/make the inner frame border invisible? Which part of the CSS would control that? Thank you,