Usage patterns
シンプルな〈物〉a simple/plain ~ (design, life, etc.)
She likes clothes with a simple design.
〈物〉をシンプルにするto make ~ simple/simplify ~
Please make the materials simpler.
シンプルに〈動詞〉to (do) simply/plainly
It's important to think about the problem simply.
シンプルな暮らしa simple lifestyle
Lately I've been trying to live a simple life.