/* Style the topnav links */
.topnav a {
float: left;
display: block;
color: #f2f2f2;
text-align: center;
padding: 14px 16px;
text-decoration: none;
}
<div class="topnav">
<a href="https://www.mammothmountain.com/winter">Mammoth</a>
<a href="https://www.skilaketahoe.com/">Lake Tahoe</a>
<a href="https://www.bigbearmountainresort.com/">Big Bear</a>
<a href="http://www.nicoleanddebbie.com/" style="float:right">Home</a>
</div>
The "a" after .topnav here means only apply these properties to anchors that are inside the topnav object
https://www.w3schools.com/cssref/pr_class_float.asp
The float property here is indicating that the element should float to the left side of the box it is in
Link
The display:block property indicates to display each object in it's own block (like it was wrapped in <p> tags
Link