CSS:

.dropzone {
    min-height: 150px;
    border: 3px solid rgba(251,137,16, 1);
    background: #ffffff;
    padding: 5px;
    text-align: center;
    border-radius: 3px;
}
.dropzone .dz-message {
    text-align: center;
    margin: 2em 0;
    color: rgba(251,137,16, 1);
    font-size: 20px;
}
.dropzone .dz-message small {
    font-size: 16px;
}

HTML:

<div class="dz-default dz-message">
<span>Drop files here to upload</span>
<br>
<small>or click to select files</small>
</div>