Yes, you can change the appearance of the widget using CSS
This will change the fonts, colors, and form of any widget elements.
This will require basic web page layout skills.
Widget styles are organized using the BEM
Each element has its own class.
To change the design of a particular item, find out its CSS class.
This is easily done through the developer's tools in the browser.
For example, in Chrome, right-click an item and choose View Code.
For the name of the day on the calendar, we defined its class - calendar-day__name.
Now let's write a simple CSS to change the background, color and font thickness:
Finally, open the widget settings on the Appearance tab.
Activate the Use custom css-styles checkbox and paste our CSS.
The result was as follows: