You can use the following syntax to select all elements with multiple CSS classes using jQuery:
$('.class1.class2');
Here, .class1.class2 is the selector that targets elements that have both class1 and class2 applied to them. In jQuery, you can chain multiple class names without spaces to select elements that contain all of those classes.
Example:
// Select elements that have both 'class1' and 'class2'
$('.class1.class2').css('color', 'red');