The FormEditionPanel requires the contenttool.css to works fine
The FormEditionPanel now add a "ametys-form-panel" css class, and this should be used in a separated css the majority of the contenttool.css
ContentTool.css should continue to keep some rules like

.contenttool .content-form-inner
{
background-color: #fafafa;
background-image: url('../../img/content/tab_bg.png');
background-repeat: no-repeat;
}