Используйте flexbox, и вы получите лучшую гибкость:
* {
box-sizing: border-box;
}
body {
display: flex;
flex-wrap: wrap;
}
h1 {
width: 100%;
}
.titles {
float: right;
border-left: solid;
border-bottom: solid;
padding: 5px 10px 5px 10px;
}
.borders {
border-style: solid;
flex-basis: 100%
}
p {
margin: 15px;
margin-top: 35px;
}
@media (min-width: 992px) {
.borders {
flex: 1;
margin: 10px; /*I added margin to all of them but you can add to only one*/
}
h1 {
margin:10px;
}
}
<h1>Module 2 Assignment</h1>
<div class="p1 borders">
<div class="titles">One</div>
<p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Dicta beatae voluptatibus veniam placeat iure unde assumenda porro neque voluptate esse sit magnam facilis labore odit, provident a ea! Nulla, minima.</p>
</div>
<div class="p2 borders">
<div class="titles">Two</div>
<p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Dicta beatae voluptatibus veniam placeat iure unde assumenda porro neque voluptate esse sit magnam facilis labore odit, provident a ea! Nulla, minima.</p>
</div>
<div class="p3 borders">
<div class="titles">Three</div>
<p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Dicta beatae voluptatibus veniam placeat iure unde assumenda porro neque voluptate esse sit magnam facilis labore odit, provident a ea! Nulla, minima.</p>
</div>