I have been making my own Habpanel look and calling it Plump as it will make all your widgets become well rounded. Whilst not finished yet, it may be of interest to others and hopefully people with more skills can help improve it. Needs a little work mainly to improve the size of text and other issues on different sized screens like Mobile vs tablet, but on 16x9 screens it is looking great here. Please post a picture of what yours looks like.
I am aiming for a simple to install theme by using a single CSS file, then you choose your own background picture to suit the season. The CSS is easy to edit and if you prefer white over a dark colour, it is very easy to change it. The line you will want to edit is --box-bg: rgb(32, 33, 37, 0.5); and the 0.5 is how transparent the widgets are and the first three are standard HTML colour codes. https://htmlcolorcodes.com/color-picker/
To try it just place the CSS file and any background picture you like into its own folder at this location. /etc/openhab2/html/themes. If you don’t like the look just remove the link and all your widets go back to their normal look. The html folder becomes the path ‘static’, the example should hopefully make it clearer if your new to this.