<form id="form" method="post" action="">

		<label for="amount">Enter amount</label>
		<div class="flex">
			<span class="currency">$</span>
			<input id="amount" name="amount" type="text" maxlength="15" />
		</div>

</form>

html {
  box-sizing: border-box;
	font-family: 'PT Sans', sans-serif;
-webkit-font-smoothing: antialiased;
}
*, 
*:before, 
*:after {
  box-sizing: inherit;
}
body {
	background-color: #f3f3f3;
}
form {
	width: 100%;
	max-width: 300px;
	margin: 60px auto;
}
form input {
	font-size: 30px;
	padding: 0;
	border: 2px solid #ccc;
	border-left: 0;
	width: 100%;
	color: #666;
	border-radius: 0 7px 7px 0;
	font-family: 'PT Sans', sans-serif;
	font-weight: bold;
}
form input:focus {
	outline: 0;
}
form input.error {
	border-color: #ff0000;	
}
form label.error {
	background-color: #ff0000;
	color: #fff;
	padding: 6px;
	font-size: 11px;
}

label {
	color: #999;
	display: block;
	margin-bottom: 10px;
	text-transform: uppercase;
	font-size: 18px;
	font-weight: bold;
	letter-spacing: 0.05em
}
.flex {
	display: flex;
	justify-content: flex-start;
}
.flex input {
	max-width: 300px;
	flex: 1 1 300px;
}
.flex .currency {
	font-size: 30px;
	padding: 0 10px 0 20px;
	color: #999;
	border: 2px solid #ccc;
	border-right: 0;
	line-height: 2.5;
	border-radius: 7px 0 0 7px;
	background: white;
}