Some CSS that will make Github Wiki content full-screen friendly (useful when presenting). Override with your browser or an extension like greasemonkey or Stylish to apply to the wikis you want.

github-wiki-override-test-double-style.css

/* and now with 100% more branding */
body { border: 10px solid #82FA32; min-height: 720px;  } 
.container { width: inherit; }
.header { display: none; }
.gh-header { padding: 30px 0px 30px 0px; background-color: black; color: white; }
.gh-header-actions { float: inherit; text-align: center; }
.btn-primary { border-color: #000; background-image: linear-gradient(#333, #000); }
.gh-header-actions .btn { float: inherit; }
.gh-header-title { padding-top: 20px; text-align: center; font-size: 4.2em; margin-right: 0px; font-weight: 100; }
.pagehead { display: none; }
#wiki-content .markdown-body { margin: 0px 20px 0px 20px; }
form { padding: 0px 20px 0px 20px; }
.repository-with-sidebar .repository-content { width: inherit; float: inherit; }
.repository-sidebar { display:none }
.gh-header-meta { display:none; }
#wiki-wrapper { margin-bottom: 20px; }
#wiki-rightbar { display: none; }
.has-rightbar #wiki-body { margin-right: 0px; }
#wiki-footer { display: none; }
.site-footer { display: none; }

github-wiki-override.css

.header { display: none; }
.pagehead { display: none; }
.repository-with-sidebar .repository-content { width: inherit; float: inherit; }
.repository-sidebar { display:none }
.gh-header-meta { display:none; }
#wiki-wrapper { margin-top: 30px; margin-bottom: 20px; }
#wiki-rightbar { display: none; }
.has-rightbar #wiki-body { margin-right: 0px; }
#wiki-footer { display: none; }
.site-footer { display: none; }