That div is basically just a container. It "holds" the loading bar and the "Click here to start" button. Think of it like this. You gave that div certain properties (like a specific position, width, and color).
<div style="position: absolute; top: 120px; width: 700px; color: white;">
Imagine that your div is a box. You have certain materials inside it (like the "Click here to start" button and the loading bar). Now, when you move the box (lets say change the top:120px to top: 500px), the contents inside it move with it. If you change the width to be smaller, the contents inside has to somehow squeeze inside to fit.
Now, lets say you remove that one line of code like you did. If you simply get rid of that line, you got rid of the box (the div). However, you aren't removing the contents inside it. That "Click here" text still exists. All you did was throw the box away but while keeping the rest of the contents that used to be inside the box. But since you threw the box away, everything is unorganized. The contents inside it are scattered around. Notice that the div has "color:white". That's why your click here button has a white font. When you got rid of that box, the click here text became black (default color). That click here text still exists on the screen but since you made the background black, it's camouflaged.