Hot answers tagged development
you can create a separate Project eg. "Common" where you include those classes. You can reference that assembly than from your other Projects. Of course, you have to ensure that this wsp is installed along your other wsps (which use that dll)
Try adding a Script Editor web part to the top of the page, edit the web part, click on "Edit Snippet", and add your style block there. SharePoint strips some things out of the main content areas, but you can effectively add style blocks, links to style sheets, script blocks, and links to script files in a Script Editor web part.
You can get (or set) the selected value from code-behind (e.g. when user clicks a button) with myDateTimeControl.SelectedDate. EDIT: See https://karinebosch.wordpress.com/sharepoint-controls/datetimecontrol-control/ for examples (SharePoint 2007, but still relevant in 2013).
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