Increasing visible text with on-click "read more"
You have lots of calls to $(".header .text"), which you can replace with calls to box:

var areaBig = box.height();


Similarly, you can simplify calls to selectors within box, such as:

// Better than: readmore = $('.header .text a[title*="meer"]')
var readmore = box.find('a[title*="meer"]');

// Better than: $(".header .text").animate(...
box.animate({ height: areaBig }, 1000, "easeInQuart", function () {
  box.find("p").css({ visibility: "visible" });
});


These changes will not only make the code easier to read but also increase execution speed.