Hello
If you use ordasvit wordpress themes - you easy may add your custom CSS styles to the theme
for that go to menu (Please check attachment img1)
Appearance->Customize
In "WorsPress Theme Customize" go to "Additional CSS" (Please check attachment img2, img3)
and there add your CSS styles
OR
If you have many styles and you better feel when work with files. You may with help FTP create file:
{yours site}/wp-content/themes/{your-ordasvit-wordpress-theme}/custom.css
or file
{yours site}/wp-content/themes/{your-ordasvit-wordpress-theme}/css/custom.css
and add yours CSS styles to these files
Regards
OrdaSoft team