Power BI - Font size in custom theme is inconsistent

Question

I just created a Theme for PowerBI using JSON. I included the following in my code to create the default font sizes:

        "label": {
            "color": "#666666",
            "fontFace": "'Trebuchet MS'",
            "fontSize": 9
        },
        "callout": {
            "color": "#666666",
            "fontFace": "Trebuchet MS",
            "fontSize": 40
        },
        "title": {
            "color": "#666666",
            "fontFace": "Trebuchet MS",
            "fontSize": 13
        },
        "header": {
            "color": "#666666",
            "fontFace": "Trebuchet MS"
        }
    },

However, all of my visuals (cards, tables, etc.) have titles with the font size of 15.6, not 13. The x and y coordinate titles have a size of 13 now, but that's it. Most "label" type text changed to 9, but in a few spots (e.g. Date input on a date filter) it didn't; the Date input was set to 8.1.

How do I ensure that all of my titles and texts will be updated correctly?

P.S. I didn't manually change any of these texts before hand; all font sizes were determined by a previous theme.

Thanks in advance.

Answer 1

The Title setting in a theme is a bot convoluted. The actual font size specified in the theme file applies to the X and Y axis. In the example below, I have set it 20 and Arial Black. You can see how it has been applied correctly to the X axis (as marked out in red).

The visual's title (marked out in blue) is also subject to this setting. However, it is increased in size by a ratio by PowerBI and will always be slightly larger. Unfortunately I don't know what that ratio is.

Note that when you resize a visual too small, PowerBI automatically (responsively) takes over control of font sizes to try make it fit. So the X Axis may still indicate 20 in the below example, but the font size is far smaller. PowerBI will reflect this by showing a little warning icon.