My images are not being displayed in a row - html

Question

In a section of my code I made a row-grid for a part that displays images but when I went to insert and look at the website its not displaying in a row format but in a column and im not sure why. I thought the problem came from it being col-sm-6 but i changed it to col-sm-12 and its still not displaying it. Any reasons why?
.site-main .project-area {
padding: 4rem 0;
}
.site-main .project-area .button-group button {
background: transparent;
border: none;
font: normal 500 16px/130px var(--lato);
text-transform: uppercase;
}
.site-main .project-area .button-group button+button {
padding-left: 3rem;
}
.site-main .project-area .grid .our-project>title h4 {
font: normal 700 25px/12px var(--lato);
}
<link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.1.3/css/bootstrap.min.css" integrity="sha384-MCw98/SFnGE8fJT3GXwEOngsV7Zt27NXFoaoApmYm81iuXoPkFOJwJ8ERdknLPMO" crossorigin="anonymous">
<section class="project-area">
<div class="container">
<div class="project title pb-5">
<h1 class="h1 text-uppercase title-h1"> Recent Projects</h1>
<h1 class="h1 text-uppercase title h1"> Quality Work</h1>
</div>
<div class="div button-group">
<button type="button" class="active">All</button>
<button type="button" data-filter=".cars">Cars</button>
<button type="button" data-filter=".character">Characters</button>
<button type="button">Food</button>
<button type="button">Activities</button>
</div>
<div class="row-grid">
<div class="col-lg-4 col-md-6 col-sm-6 element-item cars">
<div class="our-project">
<div class="img">
<img src="./img/portfolio/car.jpg" alt="car">
</div>
<div class="title py-4">
<h4 class="text-uppercase">minimul design</h4>
<span class="text-secondary">Latest, Popular</span>
</div>
</div>
</div>
<div class="col-lg-4 col-md-6 col-sm-12 element-item character">
<div class="our-project">
<div class="img">
<img src="./img/portfolio/images.jpg" alt="car">
</div>
<div class="title py-4">
<h4 class="text-uppercase">video game character</h4>
<span class="text-secondary">popular, Portfolio</span>
</div>
</div>
</div>
<div class="col-lg-4 col-md-6 col-sm-12 element-item popular">
<div class="our-project">
<div class="img">
<img src="./img/portfolio/ntfs-to-be-professional-gamer-image1.jpg" alt="car">
</div>
<div class="title py-4">
<h4 class="text-uppercase">minimul design</h4>
<span class="text-secondary">Latest, Popular</span>
</div>
</div>
</div>
<div class="col-lg-4 col-md-6 col-sm-12 element-item popular">
<div class="our-project">
<div class="img">
<img src="./img/portfolio/ntfs-to-be-professional-gamer-image1.jpg" alt="car">
</div>
<div class="title py-4">
<h4 class="text-uppercase">minimul design</h4>
<span class="text-secondary">Latest, Popular</span>
</div>
</div>
</div>
</div>
</div>
</section>

Answer 1

Changing the class row-grid to row makes it work. I don't think Bootstrap has a class called row-grid.
If you are trying to fit all the div elements into one row, just replace the col-lg-4 col-md-6 col-sm-6 and the col-lg-4 col-md-6 col-sm-12 with col