Related Posts

Hey GP

I want to show Related Posts on my "All Posts" only. but without a plugin. I don't want to use the plugin.
I want to achieve this. https://i.postimg.cc/02jj9BLY/bv.png

Just after the content and I am using this CSS TO design:

/*---[ Related Posts ]---*/
.relatedposts {
	clear:both;
    padding: 50px 0;
	position:relative;
}
.relatedposts ul {
	margin: 0;
	padding: 0;
}
.relatedposts ul li {
    background: #fff;
    box-shadow: 0 4px 10px 2px rgba(0, 0, 0, 0.1);
	float:left;
	list-style: none;
	margin:0 3% 0 0;
    position: relative;
	width:30.33%;
}
.relatedposts ul li:hover {
    box-shadow: 0 10px 30px 0 rgba(0,0,0,0.3);
}
.relatedposts ul li:nth-child(4n) { margin-right:0 }
.relatedposts img {
	float: left;
	height: auto;
	width: 100%;
}
.relatedposts .title {
	font-size:20px;
	line-height:30px;
	margin:0;
}

.relatedposts .section-heading {font-size:40px}

.relatedposts .relatedthumb {
	display: block;
	float: left;
    margin-bottom: 15px;
	width: 100%;
}
.relatedposts .related-content {
	clear:both;
    padding: 0 20px 20px;
}

How to create it on GeneratePress?