You can use

pattern="[A-Za-z].*"

Details:

• The pattern will be compiled into a ^(?:[A-Za-z].*)$ regex pattern that matches an ASCII letter at the start of string and then can contain any zero or more chars other than line break chars, as many as possible, till the end of input string
• The .* is required because the pattern regex must match the whole input

See the live demo below:

input:valid {
  color: black;
}

input:invalid {
  color: red;
}

<form name="form1">
  <input pattern="[A-Za-z].*" title="Please enter the data in correct format." />
  <input type="Submit" />
</form>

You can try the carrot symbol in regex -> Something like /^[A-Za-z]/ -> this will match the first character and tells that it must be a letter, it cannot be a space, a number or a special character.

You can write the remaining regex after that.