style.css

@media screen and (max-width: 370px) {
    .btn {
        display:block;
        float:none !important;
        width:100%;
        box-sizing: border-box;
    }
}

body {
    font-family: Verdana;
    color:white;
    background:linear-gradient(90deg, rgba(75,200,75, 0.65) 0%, rgba(60,60,200, 0.65) 100%);
}
.content {
    background:rgba(60,60,100,0.5);
    min-height:500px;
    max-width:700px;
    border-radius:15px;
    margin:auto auto;
    padding:20px;
}
.content #inputFile {
    display:none;
}
#clearBtn {
    float:right;
}
.btn {
	box-shadow:inset 0px 0px 7px 0px #29bbff;
	background:linear-gradient(to bottom, #2dabf9 20%, #0688fa 100%);
	background-size:contain;
	background-color:#2dabf9;
	border-radius:7px;
	border:2px solid rgba(255,255,255,0.75);
	display:inline-block;
	cursor:pointer;
	color:#ffffff;
	padding:6px 6px;
	text-decoration:none;
}


.btn:hover {
	background:linear-gradient(to bottom, #0688fa 5%, #2dabf9 100%);
	background-color:#0688fa;
}
.btn:active {
	position:relative;
	top:1px;
}

.preview {
    margin-top:20px;
    border:1px solid rgba(255,255,255,0.125);
    width:100%;
    min-height:400px;
}

.filerow {
    background-image:linear-gradient(to bottom,rgba(100,200,255,0.75) 0%,rgba(100,150,255,0.75) 100%);
}

.filerow > *:first-child {
    height:100px;
    width:200px;
    background-color: rgba(255, 255, 255, 0.75);
    border-radius: 10px;
    border: 2px solid;
    border-color: #008000;
    float:left;
    box-sizing: border-box;
    
}
.filerow div {
    display:inline-block;
    height:100px;
}
.filerow div:nth-child(2) {
    
}
.filerow .img {
    background-size: contain;
    background-repeat: no-repeat;
    background-position: 50%;
}

h1 {
    margin:0px;
}

@media screen and (max-width: 700px) {
    body {
        margin:0px;
    }
    .btn {
        border:none;
        border-radius:0px;
        padding:15px;
    }
    header {
        background-color:rgba(0,60,120,0.75);
        position:absolute;
        width:100%;
        margin:0px;
        top:0px;
        left:0px;
        height:100px;
        padding:15px;
        box-sizing:border-box;
    }
    .content {
        margin-top:100px;
        margin-left:0px;
        margin-right:0px;
        margin-bottom:0px;
        background:rgba(0,120,150,1);
        min-height:500px;
        max-width:700px;
        border-radius:0px;
        padding:15px;
        height:100%;
    }
}