Example 1: Using a styled horizontal rule to simulate line (browser support varies).
The lack of height causes black shadow to be faded, and the blur causes the shadow to display on all sides of line. Negative blue not supported.
Example 2: Using a 0px tall div with bottom border to simulate line.
The lack of height causes black shadow to be faded, and the blur causes the shadow to display on all sides of line. Negative blue not supported.
Example 3: Using a 1px tall div with background color to simulate line.
The lack of height causes black shadow to be faded, and the blur causes the shadow to display on all sides of line. Negative blur not supported.
Example 4: Using a 2px tall div with background color to demonstrate the difference having "height" makes on a drop-shadow. The same drop-shadown appears much darker due to the item having 1 more px of height. Negative blur not supported.
Example 5: Using a 6px tall div filled with background color, with a bottom border to simulate line.
The same drop-shadown appears muchdarker due to the item having even more height, but the added height allows negative blur values to hide 3 sides of the shadow.
Of the above options, the final one in Example 5 comes closest to simulating a line with a drop shadow, but the shadow gets curved in on both sides, and the div must have height, which can affect many layouts. (To be clear, the taller the drop shadow needs to be, the taller the div needs to be.) The difference between the "lines" below is *only* the height of the div: