Add transparency/opacity for queue sidebar (#231)

* add opacity

* add background for song metadata

* Add padding and border radius to opacity elements

* Remove font-weight transition on active lyrics (#233)

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Co-authored-by: jeffvli <jeffvictorli@gmail.com>

src/renderer/themes/light.scss

@@ -1,6 +1,7 @@
 body[data-theme='defaultLight'] {
     --icon-color: #fff;
     --main-bg: rgb(255, 255, 255);
+    --main-bg-transparent: 255, 255, 255;
     --main-fg: rgb(25, 25, 25);
     --main-fg-secondary: rgb(80, 80, 80);
     --titlebar-fg: rgb(25, 25, 25);