Problems with horizontal nav bar - html

Question

I am working on a horizontal navigation bar with a dropdown menu. I'm quite new to making codes so this is maybe a stupid question. My navigation is sticking to the left of my website, but I need it to stay in line with the text and I can't get the navigation bar threw my whole webpage how do I fix this?
photo of my website with the 2 problems:
enter image description here
nav {
position: absolute;
}
.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: 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;
width: 70px;
}
.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;
}
h1 {
margin-top: 80px;
}
<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 1

Two things in your css are giving you trouble.
nav{ position: absolute; } means this div will not fill the width.
horizontal{ margin: 40 auto;} 40 is not valid.
You MUST specify a measurement unit in CSS, so it should be 40px if I'm guessing your intention, but other units are available.
Here is amended css you can try.
nav {
width: 100%;
background-color: #006600;
}
.horizontal {
list-style-type: none;
margin: 40px auto;
width: 640px;
padding: 0;
overflow: hidden;
}

Answer 2

Step 1) Add HTML:
Example
<!-- The navigation menu -->
<div class="navbar">
<a class="active" href="#">Home</a>
Planning
Takken
Kleding
Contact
Inschrijven
</div>
And CSS:
.navbar {
width: 100%;
background-color: #555;
overflow: auto;
}
.navbar a {
float: left;
padding: 12px;
color: white;
text-decoration: none;
font-size: 17px;
width: 15%;; /* Four links of equal widths */
text-align: center;
}