Dark
い adjective
This is a single kanji with an い on the end, meaning you know it's probably an adjective. What's the adjective form of dark? It's dark.
Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You didn't learn that reading with this kanji, so here's a mnemonic to help you:
You're thrown into something dark and small. A lid is closed on top of you, and you are confused. What have you been thrown in? You find out you've been thrown in a cooler (くら). Feel afraid like you would be if you were thrown in such a dark cooler like this. Is it cold?
アレ？なんか画面がいつもより暗い。
Huh? The screen is darker than usual.
田中さんの部屋はいつも暗い。
Mr. Tanaka's room is always dark.
最近は、暗いニュースばっかりでホントにイヤになります。
I really hate all the gloomy news lately.