how to set width to 100 percent in dropdown menu

Question

hello I want to give 100% width to my dropdown menu but when I use float left or right and none is not work! How can I give width 100% to this menu?

I try give display but not work I tried for 6h and I'm very tired if some one can can help me I'm really happy :) and sorry for my bad English

my Code:

body,
ul,
li {
  margin: 0px;
  padding: 0px;
  background-color: #0CF;
}

li {
  font-family: verdana;
  font-size: 12px;
  color: #333;
  line-height: 40px;
  list-style-type: none;
  /* [disabled]list-style-image: url(../images/li.png); */
  background-color: #990;
  width: 100px;
  float: right;
  text-align: center;
  height: 40px;
  margin-left: 2px;
  display: block;
}

li ul {
  display: none;
  background-color: #CC0;
}

body ul li ul li {
  background-color: #F90;
  margin: 0px;
  padding: 0px;
  display: block;
}

li:hover {
  background-color: #CC0;
  cursor: pointer;
}

li:hover>ul {
  display: block;
}

<ul>
  <li>Item 1</li>
  <li>Item 2
    <ul>
      <li>Sub Item1</li>
      <li>Sub Item1</li>
      <li>Sub Item1</li>
    </ul>
  </li>
  <li>Item 3</li>
  <li>Item 4
    <ul>
      <li>Sub Item1</li>
      <li>Sub Item1</li>
      <li>Sub Item1</li>
    </ul>
  </li>
  <li>Item 5</li>
  <li>Item 6</li>
</ul>

---

like this image: SHOW IMAGE:

Answer 1

Change CSS

li ul {
    display: none;
    background-color: #CC0;
    width:100%;
    position: absolute;
    left: 0;
}

body ul li ul li {
    background-color: #F90;
    margin: 0px;
    padding: 0px;
    display: block;
    float: left;
}

body,
ul,
li {
    margin: 0px;
    padding: 0px;
    background-color: #0CF;
}

li {
    font-family: verdana;
    font-size: 12px;
    color: #333;
    line-height: 40px;
    list-style-type: none;
    /* [disabled]list-style-image: url(../images/li.png); */
    background-color: #990;
    width: 100px;
    float: right;
    text-align: center;
    height: 40px;
    margin-left: 2px;
    display: block;
}

li ul {
    display: none;
    background-color: #CC0;
    width:100%;
    position: absolute;
    left: 0;
}

body ul li ul li {
    background-color: #F90;
    margin: 0px;
    padding: 0px;
    display: block;
    float: left;
}

li:hover {
    background-color: #CC0;
    cursor: pointer;
}

li:hover>ul {
    display: block;
}

<ul>
        <li>Item 1</li>
        <li>Item 2
            <ul>
                <li>Sub Item1</li>
                <li>Sub Item1</li>
                <li>Sub Item1</li>
            </ul>
        </li>
        <li>Item 3</li>
        <li>Item 4
            <ul>
                <li>Sub Item1</li>
                <li>Sub Item1</li>
                <li>Sub Item1</li>
            </ul>
        </li>
        <li>Item 5</li>
        <li>Item 6</li>
    </ul>