Changing font size of tabs strip in Sublime Text 3

As outlined in the answer you linked to, find your <theme>.sublime-theme file. Open it up and search for tab_label. The section should look something like this:

{
    "class": "tab_label",
    "font.size": 12, 
    "font.face": "Ubuntu"
},

Modify it according to your preferences and save the file. You should see the changes immediately.

To change the tab dimensions you can use the following section:

{
    "class": "tabset_control",
    "tab_height": 42,
    "tab_width": 160,
    "tab_min_width": 48
},

Note: Larger font sizes (e.g. > 12pt on my system) will get cut off, even if the tab height is adjusted accordingly. This is a well-known bug.

set the following in your Preferences.sublime-settings

"dpi_scale": 2.0