How to remove unwanted gap between <ul> tag and a div - html

Question

I am having trouble trying to remove a gap between a navigation bar and a div that is supposed to show under the navigation bar.
Here's my code:
<%-- Nav Bar --%>
<ul>
<li> <a class="welcometitle"> Welcome back! <asp:Label ID="lblusuario" runat="server" ForeColor="#99ccff" Font-Bold="true"></asp:Label></a></li>
<li class="dropdown">
<div class="dropdown">
<button onclick="myFunction()" class="dropbtn"> <i class="fa fa-bars"></i> </button>
<div id="myDropdown" class="dropdown-content">
Home
About
Contact
</div>
</div>
</li>
</ul>
<%-- Iframe --%>
<div class="h_iframe">
<iframe src="inicio.aspx" name="ventana" ></iframe>
</div>
This is the CSS I'm using:
body
{
font: 14px 'Segoe UI', 'Helvetica Neue', 'Droid Sans', Arial, Tahoma, Geneva, Sans-serif;
overflow-y: hidden;
}
html, body {
height: 100%;
width: 100%;
margin: 0;
}
.h_iframe iframe {
width: 100%;
height: 100%;
margin-top: 0;
}
.h_iframe {
height: 100%;
width: 100%;
margin-top: 0;
top: 0;
z-index: -1;
padding-left: 159px;
position: fixed absolute
}
.welcometitle {
float: left;
display: block;
color: white;
text-align: center;
padding: 1px 16px;
padding-top: 12px;
text-decoration: none;
font-size: 20px;
font-weight: 500;
}
ul {
list-style-type: none;
margin: 0;
overflow: hidden;
background-color: #006cb4;
padding-left: 163px;
}
li {
float: left;
}
li a {
display: block;
color: white;
text-align: center;
padding: 14px 16px;
text-decoration: none;
}
li a:hover:not(.active) {
color: white;
}
.active {
background-color: #4CAF50;
}
.li input[type=text] {
padding: 6px;
margin-top: 8px;
font-size: 25px;
border: none;
}
img {
width: 92%;
padding-left: 8px;
margin: 0;
top: 0;
}
.dropbtn {
background-color: #111;
color: white;
padding: 16px;
font-size: 16px;
border: none;
cursor: pointer;
}
.dropbtn:hover, .dropbtn:focus {
background-color: #d4d4d4;
color: #111;
}
.dropdown {
position: relative;
display: inline-block;
}
.dropdown-content {
display: none;
position: absolute;
background-color: #f1f1f1;
min-width: 160px;
overflow: auto;
box-shadow: 0px 8px 16px 0px rgba(0, 0, 0, 0.2);
z-index: 1;
right: 0;
}
.dropdown-content a {
color: black;
padding: 12px 16px;
text-decoration: none;
/*display: block;*/
}
.dropdown a:hover {background-color: #ddd;}
.show {display: block;
position: fixed;
}
.active {
background-color: #4CAF50;
}
I have tried different things but it just doesn't seem to work. Can you find where I'm messing it up?

Answer 1

You can add some little CSS to the iframe class.
Here is the code:
.h_iframe {
margin-top: -20px;
}