Как убрать расстояние между блоками?

<div id="FULL_PAGE">
<div class="image_background">


<div class="panel_row_h_separator"></div>
<div class="panel_row_1">
<div class="graph_panel ui_panel_1">1</div>
<div class="graph_panel ui_panel_1">2</div>
<div class="graph_panel ui_panel_1">3</div>
</div>

<div class="panel_row_2">
<div class="graph_panel ui_panel_1"></div>
<div class="graph_panel ui_panel_1"></div>
<div class="graph_panel ui_panel_1"></div>
</div>

<div class="panel_row_3">
<div class="graph_panel ui_panel_1"></div>
<div class="graph_panel ui_panel_1"></div>
<div class="graph_panel ui_panel_1"></div>
</div>
<div class="panel_row_h_separator"></div>


</div>
</div>

html,body 
{
padding: 0px;
margin: 0px;
font-family: Arial;
}

.ui_panel_1 {
    padding: 10px;
    background: #222A37;
    border: 1px solid #383838;
    color: #CDCFD2;
    font-family: Arial;
    font-size: .875rem;
    vertical-align: middle;
    }
    
.image_background
{
position: fixed;
top:0px;
left:0px;
width:100%;
height:100%;
background:#e1e1e1;
}


.panel_row_h_separator
{
position: relative;
width:100%;
height: 5%;
background:perple;
}

.panel_row_1
{
position: relative;
width:100%;
height: 30%;
margin: 0 auto; 
text-align: center;
/* background:red; */
}

.panel_row_2
{
position: relative;
width:100%;
height: 30%;
margin: 0 auto; 
text-align: center;
/* background:blue; */
}

.panel_row_3
{
position: relative;
width:100%;
height: 30%;
margin: 0 auto; 
text-align: center;
/* background:yellow; */
}

.graph_panel
{
height:100%;
padding:0px !important;
margin:0px !important;
/* height: calc(100% - 20px); */
width: 20vw;
display:inline-block;

}