I know how to change the font size of the drop-downs, however, it did not change on the dashboard once i selected on item. For example, how to make the filter box/"(All)" bigger? Thanks! 
how to change Tableau Filter Content Size?
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3 Answers
The short answer is that you can change the filter box size (unfortunatelly).
The long answer is that you can try to make a simple workaround using Text/buttons in your dashboard and for each of those define a filter action (see the Tableau guide about it). Of course, it depends how many state your filter will have...if they are too many this will be a long work.
Unfortunately the filter on the dashboard will not change size. It might not be worth the effort for a workaround.
We have this functionality in latest version of Tableau, please check the version you use. Click on the top corner of filter and choose the Format filter and set control. A pane appears on the left side change the Body font to increase the filter values bigger as required.
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