Hi panchogg
T3V3 is developed with Bootstrap so the very first thing you need to know is how to use Bootstrap and LESS.
You should look at the less files in the folder: templatesja_t3v3_blankless first. The folder contains the less files like style.less, layout.less, template.less, the responsive files … Inside the folder, you can see a folder named: theme. You can create or customize themes using the files available in each theme folder.
Next, for layout customization, all files are available in folder: templatesja_t3v3_blanktpls. You can see the layout files like: default-content-left.php, default.php … and a block folder.
After customizing, please compile LESS to CSS (in the back-end setting of ja_t3v3_blank template) and please check correct Development mode (enable it or not. If you enabled it, your site runs on less file, if it is disabled, your site runs on CSS files that are compiled from LESS files as I mentioned above).
Hope this is useful for you
Thanks for using our framework.