Light themes are using badly supported urwid "bright background colors"

**Describe the bug**
The light themes of pudb use badly supported "bright background colors" https://urwid.org/manual/displayattributes.html#bright-background-colors

**To Reproduce**
Steps to reproduce the behavior:
1. Use something like urxvt or xfce-terminal (works fine on xterm or kitty)
2. Select a light theme (solarized or vim)
3. See black horror with unreadable text

**Expected behavior**
I hope that there can at least be some nice light themes that does not use the badly supported "bright background colors". Now the only ones are mono and gray-light-256, which is not a great selection.

**Screenshots**
This is the theme "vim" on urxvt:


**Solution**
We could revert to a supported background color from urwid. But I do not know how well the "light gray" works with the current light themes. The alternative is to set the background color of the themes to just "default" and let the terminal set the correct background color for the theme.

I can make also make a PR with a light theme of my own hand which relies on the background of the terminal instead.

**Versions**

This problem arised after the theme overhaul after version 2021.1. Before that, some themes used "default" instead for the background color and I have always been a happy user of midnight on my light themed terminal that worked just fine. I made a new "midday" theme in the new framework that looks just like that.

@mvanderkamp I believe you did the theme overhaul.

Compare the light themes mentioned—solarized, vim, mono, gray-light-256, and the proposed midday theme—and inspect how they set their background colors. Check the urwid documentation linked in the issue; done means a light theme remains readable in terminals with limited support for bright background colors.

Written by the indexing model from the issue text.