HTML

input text size

<style> 
	#txtbox {
    font-size: 18pt;
    height: 42px;
    width : 300px;
}
</style>

<input type="text" id="txtbox">

html input size

Syntax
<input size="number">

Example
An HTML form with two input fields with a width of 50 and 4 characters:

<form action="/action_page.php">
  <label for="fname">First name:</label>
  <input type="text" id="fname" name="fname" size="50"><br><br>
  <label for="pin">PIN:</label>
  <input type="text" id="pin" name="pin" maxlength="4" size="4"><br><br>
  <input type="submit" value="Submit">
</form>

input text size css

input[type="text"]
{
    font-size:24px;
}

change font size of input text html

<style>
#my_input{
	font-size:15px;  
}
</style>

<input id='my_input'>