When using Simple Theme Pluggin, it's no more possible to change the main jenkins logo (botom left).
Indeed, the logo is loaded with css directly in the html declaration.

Not working : index.html
<table id="main-table" height="70%" style="background-image: url(/jenkins/static/f7d903ac/images/jenkins.png); background-repeat: no-repeat; background-position: bottom left;"

Should be : index.html
<table id="main-table" height="70%">
and in css/style.css
#main-table

{ background-image: url(/jenkins/static/f7d903ac/images/jenkins.png); background-repeat: no-repeat }