Let's face it ~ you don't spend a lot of time on the 'panel' ~ but most of us like at least the activity panel to be visible.  However, with the fantastic supply of wallpaper images supplied with LXLE (plus the plenty you've collected over the years) you probably enjoy looking at them, rather than the panel, eh?

To adjust, right-click the panel and select Panel Settings.  Select the Appearance tab.

Select the Solid Color with Opacity radio button and then click the checkered button.  To achieve transparency use these settings:

Hue 261               Red 196
Saturation 12       Green 187
Value 84               Blue 213

Opacity 22%

Click OK ~ then do this for all the panels you have on your desktop so they will be synched.  (for the XP paradigm, it would be the bottom and left side panels)

Back at the Appearance tab, you can adjust the font/text color by checking the Custom Color and clicking on the color button.  I happen to like white, as I use primarily dark desktops.

The only thing about the panels that I have not been able to independently adjust is the color value of the app tabs ~ they are dependent upon the theme installed.  I would not necessarily want them to be transparent, but a bit of opacity would be nice.

Also ~ the background color of the panels will go blue occasionally when opening a program.  This drove me nuts until I figured out it seems to be related to the Random Wallpaper changer ~ simply selecting a new wallpaper by clicking on the panel icon will restore the panel transparency.

Hope this helps!