Bootstrap Theme

<style>
 #myUploader .mu-select-btn {
 background-color: #0d6efd;
 border-radius: 6px;
 color: #fff;
 }
 #myUploader .mu-dropzone {
 border: 2px dashed #0d6efd;
 background: #f0f6ff;
 }
 #myUploader .mu-progress-fill { background: #0d6efd; }
</style>

var uploader = new MultipleUpload(document.getElementById('myUploader'), {
 uploadUrl: '/api/upload'
});

Matching an existing framework

This demo passes only uploadUrl. The Bootstrap appearance is CSS mapping the component's class names onto the framework's, which is the general answer for any design system — nothing about the component has to know which one you use.

What to keep when restyling

Two things carry meaning rather than decoration: the drag-over state on the drop zone, and the visual difference between a completed file and a failed one. Those are easy to lose when swapping in a framework's neutral card styles, and both are the moments the user most needs the UI to be clear.