Hey! I did a quick play on your game and got some feedbacks on it. I think you should increase the font size for the levels for each production type or just move it to the left size of the upgrade cost. Another thing is the artifact slots that were locked. It didn't really tell me how to unlock so would be better to show it like the rest so that player can pre-plan or set a goal to unlock it since it is a pretty useful perk.
Visual wise is great. Although I suggest adding some kind of animation objects once you purchase the production upgrades. For example, once I unlock the stone golem, it should spawn a small golem that do looping animation on mining ores. Or tunnel rat where it will spawn a rat that occasionally digging. That way I can feel that I actually do put production upgrades that really do contribute to ore mining not just showing number of the ores that are mined automatically.
Think that's all from me. Looking forward to your future updates of the game! :D