You need to override your css.
1.)create css file in your module with this path
your_module/static/src/css/my_css.css
my_css.css
//put your css here to it in report.
//like,
.vertical-text {
/* Safari */
-webkit-transform: rotate(-90deg);
/* Firefox */
-moz-transform: rotate(-90deg);
/* IE */
-ms-transform: rotate(-90deg);
/* Opera */
-o-transform: rotate(-90deg);
/* Internet Explorer */
filter: progid:DXImageTransform.Microsoft.BasicImage(rotation=3);
}
2.)create xml file in your_module/views/css_view.xml
<?xml version="1.0"?>
<odoo>
<data>
<template id="assets_backend" name="mymodule css assets" inherit_id="web.assets_backend">
<xpath expr="." position="inside">
<link rel="stylesheet" href="/your_module/static/src/css/my_css.css"/>
</xpath>
</template>
</data>
</odoo>
3.)change in __manifest__.py or __openerp__.py
'data': [ 'views/css_view.xml']
and then you can use it in your report
<div class="vertical-text">Hello Vertical Texter!</div>