luci-theme-openwrt: prevent minify errors

luci-theme-openwrt: prevent minify errors

The CSS:

	padding: calc(0.125em - 1px) calc(0.5em - 1px);

produced:

	padding:calc(.125em

since minify treated it as a quad. Work around this and remove
it. The difference without it is minor.

Remove input colouring since the custom tags don't help and
the colouring makes input difficult to discern from placeholders.

Remove also -ms-backdrop definition which effectively overrides
the previous auto.

There was also an instance where 'solid red;' was truncated
to 'solid re' but I cannot reproduce this with minify.

Signed-off-by: Paul Donald <redacted>