How to right-align form input boxes?

You can use floating to the right and clear them.

form {
  overflow: hidden;
}
input {
  float: right;
  clear: both;
}
<form>
  <input name="declared_first" value="above" />
  <input name="declared_second" value="below" />
</form>

You can also set a right-to-left direction to the parent and restore the default left-to-right on the inputs. With display: block you can force them to be on different lines.

form {
  direction: rtl;
}
input {
  display: block;
  direction: ltr;
}
<form>
  <input name="declared_first" value="above" />
  <input name="declared_second" value="below" />
</form>

Or the modern way, flexbox layout

form {
  display: flex;
  flex-direction: column;
  align-items: flex-end;
}
<form>
  <input name="declared_first" value="above" />
  <input name="declared_second" value="below" />
</form>

Try use this:

<html>
<body>
   <input type="text" style="direction: rtl;" value="1">
   <input type="text" style="direction: rtl;" value="10">
   <input type="text" style="direction: rtl;" value="100">
</body>
</html>