I need help to fix a possibly messed up theme problem in Linux Mint 18.3 (Mate) desktop.

The basic desktop text appears as a possibly shadowed white, so only really works on a dark background.
I have installed various themes for the in-window content, and tried to choose from them, but it has not helped much.
(Right Click -> Change Desktop Background -> Theme Tab)

They do appear among the choices of appearance preferences except "Awaita", where the choice icon is faded out, and has a large question mark laid over it.
Clicking on it brings the alert message that the required window manager theme 'Adwaita' is not installed.
Adwaita is the default for this type of installation, and according to Synaptic, it is all there fully installed OK, and up to date. This contradicts..

I am now well confused.
The window border titles are always hard to read.
The LibreOffice spreadsheet menu toolbar is also white against very -pale grey on all themes except the black ones and the menus in LibreOffice Writer are white on white - so simply invisible!
How might we logically fix all this?

It might help if you could post or link to a screenshot to illustrate the problem. I haven't encountered anything like that with MATE and am having trouble visualizing it.

If you click the "Go Advanced" button beneath the compose post window, you get the dialogs for adding an image to your post.

Backing up what frankbell says, can you please choose the Mint-X theme then take a screenshot of the desktop that illustrates the issue and post it here. Thanks.

Thank you both for the replies.
I have managed to partly fix the "can't see anything in a white menu pull-down".
This happens when one downloads a theme that might have first served a different distro, and then not have the correct icon theme to accompany it. As example, the "Nudoka" theme requires a Fedora icon set to be present. I will remove it.

The first "screenshot1", using a supplied background called "Hill" illustrates how one longs to change the desktop icon text to have better contrast to the background, as is clearly pointed out in the "Help" section when one goes for "Customize".

Screenshot-1 also shows the "Adwaita anomaly".
It was on Mint-X Aqua, but I clicked on Adwaita to illustrate what happens.
Things do change in the desktop. See in Synaptic that I did install it!
The apt-get install adwaita command reports otherwise.
Note that the "small" Adwaita set was present first. I installed the 23.6MB "full" Adwaita theme, and then found that the "small" version could not be removed without also the "full version" being removed with it, along with a warning that to do so might render the system unstable!

We cannot choose the icon text colour.
The problem is, the tab that allows setting icon texts and features has been removed!
I still have the older Linux Mint 17 (Qiana) on another partition that was getting short of space.
There is a fifth tab that allows to choose the colours of the desktop icon texts.
You can see in screenshot-3 we now only have 4 tabs.

Come to that, it is not clear whether one can do anything with icons, such as decide the size. Maybe you can, but it is ot immediately obvious where. The washed out low contrast titlebars in the borders, and the surprising things that happen with some applications like LibreOffice or Icecat are all things I had hoped not to have to resort to lots of work to fix. I get it that these applications use their own themes, but the default setups from the past were much more immediately workable.

One of the reasons I hung in there with Linux Mint when Gnome-3 went to places I could not follow was because I could choose and set up appearances, and various functionalities to my preference. I have loved Mint for years, but if I cannot have it the way I like, and with no good information about where exactly to get at configuration scripts, I may go back to Qiana, or start looking around for something else.

I did not miss the cheer for Slack. I did not go there originally because it was all the (remarkable) work of only one guy.
Maybe I was wrong!

The remaining image was when Mint-X Aqua was fully selected.

Attached Thumbnails

     

Just a quick note that the Adwaita theme package isn't necessarily just called adwaita.

If you enter the following on the command line, you will see whether you have it installed and what it is called:

On my system, I have adwaita-icon-theme and adwaita-icon-theme-full.

Edit: Ah, I see what you are saying. The Adwaita Window Manager theme isn't installed. I'll have a look around for it...

Please see here for details on how to fix the Adwaita theme:

https://ubuntu-mate.community/t/how-...ita-theme/9039

The problem is that Adwaita appears to incorrectly handle its own Window Border theme under Metacity. Note that TraditionalOk may not exist on your system so just change the Window Border theme to any of your choosing e.g. Mint-X. You can use the default text editor xed rather than nano.

I think this is the basic naming scheme issues due to the distros with packages, they tend to give them a little twist in the name trying to make it just from them. As you can see in the final message "E: Unable to locate package adwaita" not located, therefore it never got installed because you did not tell the package manager the proper naming scheme.

https://community.linuxmint.com/soft...ita-icon-theme
then you have this type of theme
https://www.gnome-look.org/p/1012751/