.all {width:350px;position:absolute; left: 35 %;top: 35 %}
.xtop, .xbottom { display: block; background: transparent; font-size: 1px; }
.xb1, .xb2, .xb3, .xb4 { display: block; overflow: hidden; }
.xb1, .xb2, .xb3 { height: 1px; }
.xb2, .xb3, .xb4, .cont { background: White; border-left: 1px solid #00f; border-right: 1px solid #00f; }
.xb1 { margin: 0  5px; background: #00f; }
.xb2 { margin: 0  3px; border-width:  0  2px; }
.xb3 { margin: 0  2px; }
.xb4 { height: 1px; margin:  0  1px; }
.cont { padding: 1px 10px; }

.main_table {border-style: dotted; border-width: 1px; margin: 0px;padding:  0 ;}
.table_data {border-style: dotted; border-width: 1px; }
.table_data_head {text-align: center; background-color: #C1C1C1; color: white; }
.table_data_tr{background-color: #f5f5ea; }
.table_data_tr:hover{background: #CCCCFF;}
.a_table{display: block;}

<div class="all"><div class="top"><b class="xtop"><b class="xb1"></b><b class="xb2"></b><b class="xb3"></b><b class="xb4"></b></b></div>
<div class="cont">
			
			<table>
			<form method='POST' action=index.php> 
				<tr><td align = 'right'>Пользователь</td><td><select style='width:200px' name='user'> $combobox </select>  </td></tr>
				<tr><td align = 'right'>Пароль</td><td><input  type='password' name='password' style='width:200px'></td></tr>
				<tr><td colspan= 2  align='center'><input type='submit' name='enter' value='Вход'></td></tr>
						</form>
			</table>
		
</div>
<div class="bottom"><b class="xbottom"><b class="xb4"></b><b class="xb3"></b><b class="xb2"></b><b class="xb1"></b></b></div></div>