Float the clickable element to right, wrap the input
by a division and set a margin-right
to it:
CSS:
input[type="text"] { width: 100%; }
.wrapper { margin-right: 25px; }
.clickable { float: right; }
HTML:
<a class="clickable" href="#" onclick="/*call myFunc*/" >▲</a>
<div class="wrapper">
<input type="text">
</div>