Open de DOM structure in F12 developer tools and see what selectors you can use for CSS.

You want the first LI child in the QuickLaunch

All sorts of CSS selectors to get there, like:
provided the Home link is the first, otherwise you targetting will be different CSS (hint: select on href)

[id*='QuickLaunchMenu'] > ul > li:nth-child(1) {
    font-weight: bold;
    background: pink;
}

Note that the text color is on a child element, so can't be set by the LI element, you will have to extend the CSS selector to drill down deeper to the span

Open de DOM structure in F12 developer tools and see what selectors you can use for CSS.

You want the first LI child in the QuickLaunch

All sorts of CSS selectors to get there, like:
provided the Home link is the first, otherwise your targeting will be different CSS (hint: select on href)

[id*='QuickLaunchMenu'] > ul > li:nth-child(1) {
    font-weight: bold;
    background: pink;
}

Note that the text color is on a child element, so can't be set by the LI element, you will have to extend the CSS selector to drill down deeper to the span