JSFiddle - React, Tailwind, and code Playground

HTML

<div>
    <h1>I've a text in side heading with multiple lines. Want the spacing the two lines to increase, so I set a line-height. When I do this, not only does it increase space between the two lines, it also increases spacing above the first line.</h1>

    <h1>I've a text in side heading with multiple lines. Want the spacing the two lines to increase, so I set a line-height. When I do this, not only does it increase space between the two lines, it also increases spacing above the first line.</h1></div>

CSS

body {padding:30px;background:yellow;border:1px solid red;margin:0}
div{background:red;margin:0;padding:0;border:1px solid green;}
h1{line-height:2em;}
div > h1:first-child{
    margin-top:-1em;
}
div > h1:last-child{
    margin-bottom:-.25em;
}