Dropdown Menu to push content down

On my site at https://dev.fuzionbyfrances.com/, I have a submenu under “Fine Arts”. I want the submenu, when visible, to push the rest of the menu down rather than lay on top. I think I have a bit of a mess with my CSS (using a child theme) and I’m hoping someone can just send me clean CSS that will make the menu do what I want. Here’s my current CSS:

.menu-item {
    position: relative;
    display: inline-block;
}
.sub-menu {
    position: absolute;
    display: none;
    background-color: #f9f9f9;
    min-width: 160px;
    box-shadow: 0px 8px 16px 0px rgba(0,0,0,0.2);
    padding: 12px 16px;
    z-index: 1;
}
.menu-item:hover .sub-menu {
    display: block;
margin-left:5px;
}
.main-menu li {
	display: block;
	margin-top: 13px;
	font-weight: 800;
font-size: 1.2em;
	text-transform: uppercase;
	letter-spacing: 1px;
margin-left:40px;
margin-bottom:25px;
	position: relative;
}
.main-menu > li:first-child { margin-top: 0; }
.main-menu ul {margin-left: 20px; }
.main-menu a { color: #333; }
.main-menu a:hover,
.main-menu .current-menu-item > a,
.main-menu .current_page_item > a { color: #ef3e24; }
.main-menu .current-menu-item:before,
.main-menu .current_page_item:before {
	content: '\f405';
	display: block;
	font: 16px/1 "Genericons";
	color: #019EBD;
	position: absolute;
	top: -1px;
	left: -20px;
}
.credits {
float:center;
}
.main-menu:before,
.widgets:before,
.widget + .widget:before,
.credits:before {
	content: "";
	display: block;
	width: 48px;
	height: 0px;
	background: #e7e7e7;
	margin: 35px 0;
}