How to give custom menus formatting (color, etc) ?

I’m making a theme from scratch on my own and the one issue I can’t seem to beat is custom menus.

At first I tried to create a navigation menu without using WordPress’ built-in custom menus option, but the problem with this menu is that I can’t do anything fancy with it, like a dropdown menu, etc. Here is a screenshot of what it looks like without using custom menus

View post on imgur.com

I made this navmenu by putting this code in the header:

<div id="navmenu">

<ul>
<li><a>">Home</a></li>
<li><a href="https://www.wescoelectric.com/services">Services</a></li>
<li><a href="https://www.wescoelectric.com/contact">Contact</a></li>
<li><a href="https://www.wescoelectric.com/news">News</a></li>
<li><a href="https://www.wescoelectric.com/about">About</a></li>
</ul>
 </div>

So since I wasn’t able to do drop down menus with this, I decided to try the custom menus.

I enabled custom menu support and removed the above code, but now I’m left with a barebone menu that I have no idea how to customize (add color, change location, change font, background, etc). I searched on google but I haven’t been able to find anything online for this because 99% of people asking questions are using an already created theme, and as such their themes already have that code built in. This is what it looks like at the moment:

View post on imgur.com

To reiterate, I want to change the navigation menu in that screenshot to look something more like the first screenshot.I hope what I wrote makes sense, I’m just completely new at this stuff. Thanks for any help!