Two questions

@crease123:
1) How do I center-justify the captions for my images? Right now, they are all left-justified.
— You can add the following CSS in “Appearance => Theme Options => Custom CSS” box.
.wp-caption p.wp-caption-text { text-align: center; }

2) For the search bar in the header, how do I make the area where you type gray? My header background color now is white, and the search bar type area can’t be seen because of that.
— You can add the following CSS in “Appearance => Theme Options => Custom CSS” box.
#sidebar form.searchform input { background-color: #f5f5f5; }

@crease123: Sorry. Correction on my previous CSS for header. You can replace your CSS
#sidebar form.searchform input { background-color: #f5f5f5; }
With the following CSS
#header .social-search form.searchform input { background-color: #f5f5f5; }

@crease123: Try adding this in your Custom CSS box. If this doesn’t work then sorry you need to hire css developer to work for you.

#header #mainmenu ul li:last-child {
    border-right: none;
}
#header #mainmenu ul li a:last-child {
    padding: 0 17px;
}