Your textbox code:
<input type="text" class="textboxclass" />
Your CSS code:
input[type="text"] {
height: 10px;
width: 80px;
}
or
.textboxclass {
height: 10px;
width: 80px;
}
So, first you select your element with attributes (look at first example) or classes(look last example). Later, you assign height and width values to your element.