problems with dropdown nav bar - css

Question

I'm having problems with my navbar. The process of making one is already done, but when I hover over my nav and my subnav appears, all the text below it moves down.
How do I fix this?
Here is a code snippet which demonstrates the problem, hover over TAKKEN to see the issue:
.horizontal {
list-style-type: none;
margin: 40 auto;
width: 640px;
padding: 0;
overflow: hidden;
}
.horizontal>li {
float: left;
}
.horizontal li ul {
display: none;
margin: 0;
padding: 0;
list-style: none;
position: relative;
width: 100%;
}
.horizontal li:hover ul {
display: block;
}
.horizontal li a {
display: block;
text-decoration: none;
text-align: center;
padding: 22px 10px;
font-family: arial;
font-size: 8pt;
font-weight: bold;
color: #FFFFFF;
text-transform: uppercase;
border-right: 1px solid #607987;
background-color: #006600;
letter-spacing: .08em;
}
.horizontal li a:hover {
background-color: darkorange;
color: #a2becf
}
.horizontal li:first-child a {
border-left: 0;
}
.horizontal li:last-child a {
border-right: 0;
}
<nav id="mainnav">
<ul class="horizontal">
<li>Home</li>
<li>Planning</li>
<li>Takken
<ul>
<li>Kapoenen</li>
<li>Kawellen</li>
<li>Kajoo's</li>
<li>Jojoo's</li>
<li>Givers</li>
<li>Jin</li>
<li>Akabe</li>
</ul>
</li>
<li>Kleding</li>
<li>Contact
<ul>
<li>Leiding</li>
<li>Verhuur</li>
</ul>
</li>
<li>Inschrijven</li>
</ul>
</nav>
Here is some text below the nav.
Image showing the problem

Answer 1

Try giving a fixed width to the li elements.
Check this:
.horizontal {
list-style-type: none;
margin: 40 auto;
width: 640px;
padding: 0;
overflow: hidden;
}
.horizontal > li {
float: left;
width: 6rem;
}
.horizontal li ul{
display: none;
margin: 0;
padding: 0;
list-style: none;
position: relative;
width: 100%;
}
.horizontal li:hover ul {
display: inline-block;
}
.horizontal li a{
display: block;
text-decoration: none;
text-align: center;
padding: 22px 10px;
font-family: arial;
font-size: 8pt;
font-weight: bold;
color:#FFFFFF;
text-transform: uppercase;
border-right: 1px solid #607987;
background-color: #006600;
letter-spacing: .08em;
}
.horizontal li a:hover {
background-color: darkorange;
color:#a2becf
}
.horizontal li:first-child a { border-left:0; }
.horizontal li:last-child a { border-right:0; }
<nav id="mainnav">
<ul class="horizontal">
<li>Home</li>
<li>Planning</li>
<li>Takken
<ul>
<li>Kapoenen</li>
<li>Kawellen</li>
<li>Kajoo's</li>
<li>Jojoo's</li>
<li>Givers</li>
<li>Jin</li>
<li>Akabe</li>
</ul>
</li>
<li>Kleding</li>
<li>Contact
<ul>
<li>Leiding</li>
<li>Verhuur</li>
</ul>
</li>
<li>Inschrijven</li>
</ul>
</nav>

Answer 2

There appear to be 2 style-related problems with your nav.
Elements are being shifted to the side when you hover over TAKKEN.
This is happening because the text KAPOENEN and KAWELLEN is longer and therefore wider than TAKKEN. The quickest fix would be to define a specific width for each of the items in your nav.
Any text below the nav moves down as soon as one of the subnavs open.
To solve this problem, you need to give your nav an absolute position, and add a placeholder div to just above it in your HTML.
Run the code snippet below to see a demonstration of both points. I've marked all my changes in the CSS using comments.
/* New code */
#placeholder {
height: 100px;
}
nav {
position: absolute;
top: 5px;
}
/* End new code */
.horizontal {
list-style-type: none;
margin: 40 auto;
width: 640px;
padding: 0;
overflow: hidden;
}
.horizontal>li {
float: left;
}
.horizontal li ul {
display: none;
margin: 0;
padding: 0;
list-style: none;
position: relative;
width: 100%;
}
.horizontal li:hover ul {
display: block;
}
.horizontal li a {
display: block;
text-decoration: none;
text-align: center;
padding: 22px 10px;
font-family: arial;
font-size: 8pt;
font-weight: bold;
color: #FFFFFF;
text-transform: uppercase;
border-right: 1px solid #607987;
background-color: #006600;
letter-spacing: .08em;
/* New code */
width: 80px;
}
.horizontal li a:hover {
background-color: darkorange;
color: #a2becf
}
.horizontal li:first-child a {
border-left: 0;
}
.horizontal li:last-child a {
border-right: 0;
}
<div id="placeholder"></div>
<nav id="mainnav">
<ul class="horizontal">
<li>Home</li>
<li>Planning</li>
<li>Takken
<ul>
<li>Kapoenen</li>
<li>Kawellen</li>
<li>Kajoo's</li>
<li>Jojoo's</li>
<li>Givers</li>
<li>Jin</li>
<li>Akabe</li>
</ul>
</li>
<li>Kleding</li>
<li>Contact
<ul>
<li>Leiding</li>
<li>Verhuur</li>
</ul>
</li>
<li>Inschrijven</li>
</ul>
</nav>
Here is some text under the nav.