。
I like the simple aspect of her dress.
Literal
I [topic-は] her [attributive-の] dress [attributive-の] simple [nominalizer-なところ] [subject-が] like-[copula-だ].
Notice the metaphorical use of ところ ('place') — attached to adjectival modifier, it doesn't mean a physical place but 'an aspect, a part, a point about' the thing. ~のシンプルなところ literally 'the simple place of,' meaning 'the simple aspect/feature of.' This is a very productive pattern for picking out a quality you like or dislike. シンプル is a loanword na-adjective; note the な before ところ.