Alternative Symbols for cellsuffix feedback

I am new to CL, so be patient…
I have started to create an activity that checks if factor pairs are truly a multiple of a pre-determined value (24 in my example) and that it adds to equal 11 (start of a quadratic factoring activity). The sample I used to start to create this gives a nice green checkmark as feedback in the appropriate cell when it is correct, but the otherwise is just empty " ". I could use just a text “X”, but I’d rather have a red “x” so it is a similar style to the green checkmark. How/where do I get symbols like the green checkmark to use as my otherwise feedback?

Here is the sample activity.

I’ve used this site to copy-paste.
Here’s one from the emoji section :x:. Just note that they don’t all necessarily display the same on different devices. I’ve noticed the nice green checkmark was just grey text on my students’ chromebooks on site.

Thanks so much, Daniel. This worked perfectly. I’ll check it out with one of my students to see how it appears on their chromebooks.