Hello @Jake_Slack!
I don't think it's possible to apply selectors to Retool's DOM elements using JS at runtime.
You can use {{ }} to reference retool values when writing custom CSS.
The buttons have the date set as the aria-label so you could do something like this.
{{ query4.data.map(d => [aria-label="${d}"] {background-color: blue !important;}).join('') }}
query4.data is an array -> ['2025-01-01', '2025-01-04']
Retool may change selectors / DOM structure with any update though which can break custom CSS. So it would probably to build a custom component if you want something more reliable.
I can make a feature request to make custom styling for specific days inside our calendar component easier as well and will keep you posted on that!
