At first make a class

.lineheight_p { line-height: 2.2em;
font-size: 40px; }

Finally paste lineheight_p in ADDITIONAL CSS CLASS(ES)

How to Change Font Size, Color, Background of a specific letter

In WordPress, if you want to change the font size of a specific letter, you would typically use a combination of HTML and CSS.

Here’s a step-by-step process:

Identify the Letter in the Content:

Wrap the specific letter in a span tag.

<span class="special-letter">A</span>pple

This would target the letter “A” in the word “Apple”.

Styling the Letter:

Add custom CSS to style the wrapped letter.
There are several ways to add custom CSS in WordPress, one of the most common methods is via the Customizer.
Go to Appearance > Customize > Additional CSS and add:

.special-letter {
    font-size: 30px;            /* Adjust to your desired size */
    color: red;                /* Adjust to your desired font color */
    font-weight: bold;         /* Makes the letter bold */
    background-color: yellow;  /* Adjust to your desired background color */
    padding: 2px;              /* Optional: add some space around the letter */

The padding property is optional, but it can give some space around the letter, making the background color more evident.