To summarize what
t4ewk said above, this should be your thought process:
1) Pick a card, any card
2) See what they play, calculate their total
3) Roll it back (use mousewheel to go backwards)
4) If you can beat them, beat them with the lowest card possible
5) If nothing in your hand can beat them, throw away your lowest card and lose that round
6) ???
7) Profit
Also as
t4ewk said, this implementation is buggy af, more or less devoid of significant strategy, time consuming, and not particularly rewarding to win. Considering there are 60 cards, I decided to just look at the images.