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<input type="file" id="file-upload" />
<label for="file-upload">Upload a file</label>
input[type="file"] {
opacity: 0; /* make transparent */
z-index: -1; /* move under anything else */
position: absolute; /* don't let it take up space */
}
input[type="file"]:focus + label {
outline: 2px solid; /* example focus style */
}