I was trying to add some basic and custom web parts to a SharePoint web part page and realized that although I could scroll through all the web parts in the gallery, I could not find the “Add” button at the bottom of the page. In I could not see any of the usual buttons or links at the bottom of the page either.
What happened was that we had created a custom theme that would apply to all web pages in the site; in the process we had modified some CSS files with some additional styles. The styles also apply to the dialog page that comes up when you click “Add a Web Part”. The specific style that caused the dialog not to show the buttons due to its width element is shown below. Please note the buttons are actually created but are not fully visible due to the style below.
#aspnetForm {margin:20px auto;width:960px;background-color:white;border:2px solid #435380;}
In my case, if you remove the WIDTH element the buttons show up properly. I talked to my SharePoint designer Phil Foss (http://philfoss.com ) who then modified the styles which then made the button visible again.
NOTE:The “Add Web Parts” page (webpartgallerypickerpage.aspx) is a page that exists in the layouts folder to which styles are applied as well. You can find a link to the web part gallery page if you look at the source of the page that you are editing in your browser (Search for "Add a Web Part").