Check out example codes for "custom input file button". It will help you in understanding the concepts better.

Code Example 1

<style>
div.fileinputs {
	position: relative;
}

div.fakefile {
	position: absolute;
	top: 0px;
	left: 0px;
	z-index: 1;
}

input.file {
	position: relative;
	text-align: right;
	-moz-opacity:0 ;
	filter:alpha(opacity: 0);
	opacity: 0;
	z-index: 2;
}
</style>
<div class="fileinputs">
	<input type="file" class="file" />
	<div class="fakefile">
		<input />
		<img src="search.gif" />
	</div>
</div>

Code Example 2

<input type="file" class="custom-file-input">

Code Example 3

<input id="file-upload" class="p-0" required name="photo" type="file" accept="image/jpeg, image/png, application/pdf" />

::-webkit-file-upload-button {
    background: #FF4B2B;
    color: white;
    padding: 8px 25px;
    font-size: 10px;
    border-radius: 20px;
    box-shadow: 0 4px 6px rgba(50, 50, 93, 0.11), 0 1px 3px rgba(0, 0, 0, 0.08);
    border-color: #FF4B2B;
    transition: all 0.15s ease;
    letter-spacing: 1px;
    box-sizing: border-box;
    outline: none;
    cursor: pointer;
    line-height: 1.5;
    display: inline-block;
    font-weight: bold;
    text-align: center;
    white-space: nowrap;
    vertical-align: middle;
    user-select: none;
    border: 1px solid transparent;
}

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