Why my pdf report is not taking the CSS styles well in Odoo?

I am using Odoo 10 in Ubuntu Server. I am trying to print my quotation report in pdf format using wkhtmltopdf. But the design doesn't look nice. It looks like the CSS is not working

I have tried to change some XML file inside mypath/addons but it doesn't work

Here's my quotation pdf file:

1st Possible Reason

If your report doesn't have styles try to add some of these parameters in Settings > Parameters > System parameters:

• web.base.url: <IP address>:<Port>
• web.base.url.freeze: True. If this parameter is not used then if the administrator log in Odoo the web.base.url parameter is updated with the current addres that's in the address bar.
• report.url: <IP address>:<Port>. This should be used if web.base.url parameter is not enough to make it work. Usually this url should be: http://127.0.0.1:8069

2nd Possible Reason

Also it is possible that the package wkhtmltopdf is not well installed or it has not the correct version. Here you can check the release 0.12.5 that works well with Odoo v10 and later versions.

3rd Possible Reason

As it is suggested here, the report contents must be inside this element with that specific class: <div class="page">