Help - Is this dress too summery for party tonight?

[polyhymnia]

Going to a birthday party tonight, actually for a 30th, but thrown by the mum at her home and at least as many guests the mum's and my age as in 30s.

They're hoping most of it can be held in garden. Also told not to dress in our best, though think that doesn't mean come in jeans.

Thinking of wearing this with cropped cardi:

www.boden.co.uk/en-GB/Clearance/Womens-Dresses/Smart-Day-Dresses/WH615/Womens-Seville-Dress.html

Have it in the blue and the green (bought in sale) and feel it suits me and am comfortable wearing it. But wonder if it looks too summery/ holiday-ish for a party in September in London suburbs?

Alternative would probably be these trousers:

www.boden.co.uk/en-GB/Womens-Trousers-Jeans/Trousers/WM357/Womens-Chelsea-Turn-up.html?NavGroupID=19

in black, with interesting long top - black background with interesting and quite colourful pattern over the upper part of it (Marina Rinaldi, ie Maxmara, but can't link it).

Votes, please!

I think the dress would be lovely as long as you won't get cold.

I think either are fine.

The dress is fine.

lovely dress. It's still summer dress weather imo.

the dress. make the most of the last of the summer.

Thanks for the responses - the dress it is, but will take along my leather or my denim short jacket as well as the cropped cardi in case it gets too chilly.