Automatically disabling buttons when player doesn't have enough mana?

I'm working on a sheet for an upcoming game (Unity). Part of the project is letting the players add their powers (think 4e-style abilities) to a repeating list. These powers have "mana" costs associated with them (every class resource is called something different, but let's call it mana for simplicity's sake). Each power has a checkbox (which I plan on styling like a button) which deducts the cost from the player's mana pool. I also have functions watching to make sure the values don't go below 0 or above the max.  My issue is that I want to disable the "spend power" checkbox when the player doesn't have the mana to spend. For instance, I have the made-up power Justice set up on my sheet. It has a cost of 3, and the player only has 2 mana. In this situation, I want the spend mana button to be greyed out/disabled/whatever. I can't figure out how to make this work - a lot of the CSS hide/show/disable tricks require the player to actively click on a checkbox, but I want this to happen automatically (I have a loop that checks all of the powers any time the player's mana value changes, to re-evaluate what is affordable and what isn't). Any help would be greatly appreciated!

You could have a sheetworker that watches the mana pool and on change cycle through all the powers and any power that has a higher mana cost than exists in the pool, hide the checkbox and display a span that looks like the checkbox, but is a different color...

That's sort of what I'm doing, but how do you hide/disable buttons via sheet workers? As far as I know, all you can do is change attribute values, and not any properties of the elements. If there was a way to check boxes via sheet workers, that would work, but changing the value doesn't trigger :checked elements in the CSS etc.

You have a CSS rule that hides the styled field or div based on the status of a checkbox. It's described on the CSS Wizardry page of the wiki

Eric S. said: That's sort of what I'm doing, but how do you hide/disable buttons via sheet workers? As far as I know, all you can do is change attribute values, and not any properties of the elements. If there was a way to check boxes via sheet workers, that would work, but changing the value doesn't trigger :checked elements in the CSS etc. Setting a checkbox value does make it checked, as long as the value is the value of the checkbox. For example: <input type="checkbox" value="1" name="attr_tester" /> Using a sheet worker to set tester = 1 will make that checkbox checked, setting to a value other than 1 will make it unchecked. With that checkbox being checked, the CSS will trigger—at least it does for me.   NOTE : You want to be sure to give the checkbox a value for when it is checked.  If you don't specify a value, then that may be why you aren't seeing it as checked. I've also found it easier to make sure the value is something other than 0.

Well, crap. I thought I'd already tried out the checkbox value check/uncheck thing, but I suspect I wasn't setting the value properly when setting it up in the first place. Thanks for all your help!