How do I make this image show properly?

So, I want to make this image show fully. Heres my code so far:

Link: https://summit.tahaparacha1.repl.co/

HTML:

        <div class="header">
        <h1>Learn Mathmatics In Minutes!</h1>
        <h3>Increase your knowledge with Summit! Summit allows you discover the endless possiblities you probably thought never exsisted. Start learning for free at your own pace now, or scroll down to see what we offer.</h3>

        <a class="grow "href="#">Start Learning</a>
    </div>

CSS:

.header {
    background-image: url("images/SummitHome1.jpg");
    width: 100%;
    height: 100vh;
}