[BUG] Can't change Float ToggleTerm's background

### Is there an existing issue for this?

- [X] I have searched the existing issues

### Current Behavior

Currently with a set up like this:

```lua
return {
'akinsho/toggleterm.nvim',
version = '*',
config = function()
require('toggleterm').setup({
autochdir = true,
open_mapping = [[]],
shade_terminals = false,
hide_numbers = true,
start_in_insert = true,
direction = 'float',
persist_size = true,
persist_mode = true,
close_on_exit = false,
float_opts = {
border = 'curved',
winblend = 0,
title_pos = 'center',
},
highlights = {
FloatBorder = {
guifg = '#e67e80',
},
Normal = {
guibg = '#ffffff',
},
NormalFloat = {
link = 'Normal',
},
},
})
end,
}
```

Does not seem to change the guibg to FFFFFF. It stays as my current colorscheme's background.

### Expected Behavior

I expect it to turn all white.

### Steps To Reproduce

Use my settings of:

```lua
return {
'akinsho/toggleterm.nvim',
version = '*',
config = function()
require('toggleterm').setup({
autochdir = true,
open_mapping = [[]],
shade_terminals = false,
hide_numbers = true,
start_in_insert = true,
direction = 'float',
persist_size = true,
persist_mode = true,
close_on_exit = false,
float_opts = {
border = 'curved',
winblend = 0,
title_pos = 'center',
},
highlights = {
FloatBorder = {
guifg = '#e67e80',
},
Normal = {
guibg = '#ffffff',
},
NormalFloat = {
link = 'Normal',
},
},
})
end,
}
```

### Environment

```Markdown
- OS: Sonoma 14.5
- neovim version: NVIM v0.10.0
- Shell: zsh
```

### Anything else?

_No response_