JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">
    <div class="leftone">Project</div>
    <div class="leftone">About the Project</div>
    <div class="leftone">Contact Us</div>
    <div>Mailbox</div>
</div>

CSS

.container {
    display: flex;
    justify-content: flex-start;
    flex-direction: row;
    align-items: center;
    /* width: 100%; */
    height: 50px;
    background: #333;
    padding: 15px;
    color:#ddd;
    padding:10px;
}
.container> .leftone{
  margin-left:20px;
}


.container div:last-child {
	margin-left: auto;
}