溢出-x | overflow-x

/* Content is not clipped */
overflow-x: visible;

/* Content is clipped, with no scrollbars */
overflow-x: hidden;

/* Content is clipped, with scrollbars */
overflow-x: scroll;

/* Let the browser decide */
overflow-x: auto;

/* Global values */
overflow-x: inherit;
overflow-x: initial;
overflow-x: unset;

visible | hidden | scroll | auto

<ul>
  <li><code>overflow-x:hidden</code> — hides the text outside the box
    <div id="div1">
      ABCDEFGHIJKLMOPQRSTUVWXYZABCDEFGHIJKLMOPQRSTUVWXYZ
    </div>
  </li>

  <li><code>overflow-x:scroll</code> — always add a scrollbar
    <div id="div2">
      ABCDEFGHIJKLMOPQRSTUVWXYZABCDEFGHIJKLMOPQRSTUVWXYZ
    </div>
  </li>

  <li><code>overflow-x:visible</code> — displays the text outside the box if needed
    <div id="div3">
      ABCDEFGHIJKLMOPQRSTUVWXYZABCDEFGHIJKLMOPQRSTUVWXYZ
    </div>
  </li>

  <li><code>overflow-x:auto</code> — on most browsers, equivalent to <code>scroll</code>
    <div id="div4">
      ABCDEFGHIJKLMOPQRSTUVWXYZABCDEFGHIJKLMOPQRSTUVWXYZ
    </div>
  </li>
</ul>

#div1, #div2, #div3, #div4 {
  border: 1px solid black;
  width:  250px;
  margin-bottom: 12px;
}

#div1 { overflow-x: hidden;}
#div2 { overflow-x: scroll;}
#div3 { overflow-x: visible;}
#div4 { overflow-x: auto;}