How would you make two <div>s overlap?

I need two divs to look a bit like this:

    |               |
 ---|    LOGO       |------------------------
|   |_______________|  LINKS                |
|             CONTENT                       |

What's the neatest/most elegant way of making them overlap neatly? The logo will have a fixed height and width and will be touching the top edge of the page.

Just use negative margins, in the second div say:

<div style="margin-top: -25px;">

And make sure to set the z-index property to get the layering you want.

I might approach it like so (CSS and HTML):

html,
body {
  margin: 0px;
}
#logo {
  position: absolute; /* Reposition logo from the natural layout */
  left: 75px;
  top: 0px;
  width: 300px;
  height: 200px;
  z-index: 2;
}
#content {
  margin-top: 100px; /* Provide buffer for logo */
}
#links {
  height: 75px;
  margin-left: 400px; /* Flush links (with a 25px "padding") right of logo */
}

<div id="logo">
  <img src="https://via.placeholder.com/200x100" />
</div>
<div id="content">
  
  <div id="links">dssdfsdfsdfsdf</div>
</div>

With absolute or relative positioning, you can do all sorts of overlapping. You've probably want the logo to be styled as such:

div#logo {
  position: absolute;
  left: 100px; // or whatever
}

Note: absolute position has its eccentricities. You'll probably have to experiment a little, but it shouldn't be too hard to do what you want.

Using CSS, you set the logo div to position absolute, and set the z-order to be above the second div.

#logo
{
    position: absolute:
    z-index: 2000;
    left: 100px;
    width: 100px;
    height: 50px;
}

If you want the logo to take space, you are probably better of floating it left and then moving down the content using margin, sort of like this:

#logo {
float: left;
margin: 0 10px 10px 20px;
}

#content {
margin: 10px 0 0 10px;
}

or whatever margin you want.