You can easily create three floating boxes side by side. However, when you add something that enlarges the width of each box (e.g. padding or borders), the box will break. The box-sizing property allows us to include the padding and border in the box's total width (and height), making sure that the padding stays inside of the box and that it does not break.
If you hire a professional to code a complicated site, remember that programmers are not necessarily graphic designers. The most eye-catching sites out there have been made by or with the input of someone involved in graphic design. The best advice, especially for a professional site, is to use the right team for the job: designers design the look and feel of the site; programmers do all the stuff under the hood to make it work; marketers position the site and make sure it's relevant; and writers write the copy. how to make a website