Do you want this to affect just the title and description (aka site branding), or the menu as well?

For the title and description only, add the following to ADDITIONAL CSS box in Customizer:

.site-branding {
background-color: #fff;
opacity: 0.5;
padding-left: 10px;
padding-right: 10PX;
}

Feel free to change the background color, opacity and padding values to your heart’s desire.

If you want this to affect the menu as well, use the following instead:

.site-header .tg-header-container {
background-color: #fff;
opacity: 0.5;
}

(Here we don’t need the paddings because there’s ample empty space around the container already)

If you want to apply this to the entire header, the safest class to target would be tg-site-header-bottom. Use:

.tg-site-header-bottom {
background-color: #fff;
opacity: 0.5;
}

And you may want to remove the remnant image at the bottom with this:

.tg-site-header {
padding-bottom: 0px;
}

Good luck!

Thank you SO much for your help! I have used the second solution you provided (to include the menu) and it has worked perfectly!

Thank you for taking the time to help me with this!

By the way, here’s one more low-hanging fruit to fix on your website.

All your inner pages are using the addresses beginning with https://just2001.temp.domains/~corylove/, instead of the https://corylovesbeer.com/

To fix this, go to SETTINGS => GENERAL, and change both WordPress Address (URL) and Site Address (URL) to https://corylovesbeer.com (take care to enter the correct address, as a mistake could break the site!)

Good luck!