I have a typo3 website where you can find :

<link rel="stylesheet" type="text/css" 
href="fileadmin/templates/mysite.com/css/style.css" media="all" />

style.css contains :

@import "structure.css";
@import "menu.css "; 
@import "content-style.css";
@import "submenu.css";
@import "top.css";
@import "footer.css";
@import "recherche.css";
@import "dropdown-sitemap.css";
@import "powermail.css";
@import "tt_news.css";

textarea.powermail_solutiondetlphonie
{
    display:normal;
}

.powermail_pagebrowser
{
    display:none;
}

.tx_powermail_pi1_fieldwrap_html_checkbox_title
{
    font-weight:bold;
}

mod_page speeds decides to inline the content of this css file in the page as 
is ; however it should add the path of the original css before as then the css 
file cannot be found...

I.e it should write :

@import "fileadmin/templates/mysite.com/css/structure.css";
@import "fileadmin/templates/mysite.com/css/menu.css "; 
@import "fileadmin/templates/mysite.com/css/content-style.css";
@import "fileadmin/templates/mysite.com/css/submenu.css";
@import "fileadmin/templates/mysite.com/css/top.css";
@import "fileadmin/templates/mysite.com/css/footer.css";
@import "fileadmin/templates/mysite.com/css/recherche.css";
@import "fileadmin/templates/mysite.com/css/dropdown-sitemap.css";
@import "fileadmin/templates/mysite.com/css/powermail.css";
@import "fileadmin/templates/mysite.com/css/tt_news.css";

textarea.powermail_solutiondetlphonie
{
    display:normal;
}

.powermail_pagebrowser
{
    display:none;
}

.tx_powermail_pi1_fieldwrap_html_checkbox_title
{
    font-weight:bold;
}

instead of :

@import "structure.css";
@import "menu.css "; 
@import "content-style.css";
@import "submenu.css";
@import "top.css";
@import "footer.css";
@import "recherche.css";
@import "dropdown-sitemap.css";
@import "powermail.css";
@import "tt_news.css";

textarea.powermail_solutiondetlphonie
{
    display:normal;
}

.powermail_pagebrowser
{
    display:none;
}

.tx_powermail_pi1_fieldwrap_html_checkbox_title
{
    font-weight:bold;
}