Cant stick a div to the bottom of his parent div - html

Question

hello everyone i am trying to create
a div that will Functioned as the bottom border of
this form, like this:
The problem is that it only works if I use
margin-top and i dont want to use that.
this is what i am getting now:
my css:
#form_div
{
position: absolute;
top:67px;
left:450px;
height:550px;
-moz-box-shadow: 2px 3px 45px #000000;
-webkit-box-shadow: 2px 3px 45px #000000;
box-shadow: 2px 3px 45px #000000;
border-radius: 15px;
-moz-border-radius: 15px;
-webkit-border-radius: 15px;
}
#bottum_border
{
border-bottom:1px solid red;
cursor: e-resize;
margin-top: 43px;
}
my html:
<div id="form_div" class="black_background_solid" >
<div id="form_headline" class="light_black">Contact Us</div>
<div id='n_1_conteiner' class='field_conteiner'>
<div id='n_1_lbl' class="field_name">Name:</div>
<input id='n_1_textbox' class='textbox gray white_text' type='text'/>
<a id='n_1_edit_btn' class='edit_button'>Edit</a>
<a id='n_1_drop_btn' class='drop_button'>Drop</a>
<div id='n_1_border' class='fakeHr line_border_color_black'></div>
</div>
<div id='n_5_conteiner' class='field_conteiner'>
<div id='n_5_lbl' class='field_name'>Message:</div>
<textarea id='n_5_tbx' class='text_area gray white_text' rows="2" cols="30">
</textarea>
<a id='n_5_edit_btn' class='edit_button'>Edit</a>
<a id='n_5_drop_btn' class='drop_button'>Drop</a>
</div>
<div id='results_div'>
<div id='submit_btn' class="button red_gradient" onclick="Validate()">
Submit</div>
</div>
<div id='bottum_border'></div>
</div>
exact codes pasted in fiddle http://jsfiddle.net/z982S/

Answer 1

Try removing height (Use padding/margin instead) from: #form_div & add following to #bottum_border
#bottum_border
{
position:relative;
bottom: 0;
}

Answer 2

#bottum_border
{
border-bottom:1px solid red;
cursor: e-resize;
position: absolute;
bottom: 0px;
width: 100%;
}
Check fiddle http://jsfiddle.net/Zd4fr/

Answer 3

If you want something like 1st image then Why don't you use border-bottom directly to the form_div?
#form_div
{
border-bottom:1px solid red;
}

Answer 4

You need something like this:
#form_div
{
position: relative;
}
#submit_btn
{
position: absolute;
bottom:0;
}
This positions the button to the bottom of the form.