Whats the CSS to make something go to the next line in the page?

How can I make an element automatically be positioned on a new line in the page? In HTML I could use <br>, but how do I add something like a line-break in CSS?

Say I have the following code for example:

<p>Lorem ipsum dolor sit amet,
   <span id="elementId">consectetur adipisicing elit.</span>
   Magni totam velit ex delectus fuga fugit</p>

The span is still positioned on the same line as the rest of the text. How can I move the span text on a new line purely through CSS?

Another example is when using display: inline-block or float:

<div class="smalldiv">Lorem ipsum dolor sit amet</div>
<div class="smalldiv">Lorem ipsum dolor sit amet</div>
<div class="smalldiv" id="elementId">Lorem ipsum dolor sit amet</div>
<div class="smalldiv">Lorem ipsum dolor sit amet</div>

.smalldiv {
    display: inline-block; // OR
    float: left;
}

How can I move one of the <div>s on a new line to create a new row?

There are two options that I can think of, but without more details, I can't be sure which is the better:

#elementId {
    display: block;
}

This will force the element to a 'new line' if it's not on the same line as a floated element.

#elementId {
     clear: both;
}

This will force the element to clear the floats, and move to a 'new line.'

In the case of the element being on the same line as another that has position of fixed or absolute nothing will, so far as I know, force a 'new line,' as those elements are removed from the document's normal flow.

Have the element display as a block:

display: block;

It depends why the something is on the same line in the first place.

clear in the case of floats, display: block in the case of inline content naturally flowing, nothing will defeat position: absolute as the previous element will be taken out of the normal flow by it.