fix: Apply dark theme to the slide left icon (#857)

### Fix
* Remove the `fill="black"` property from the svg file
### ChangeLog
* Apply the IconColors to the SlideLeft icon

Author: HoonBaek

src/svgs/_README_FOR_ADDING_ICON.md

@@ -0,0 +1,32 @@
+# Add Icon
+
+When you add icon.svg files into this directory, there are things that you have to remember.
+
+- You should remove the properties `width`, `height`, and `fill`.
+  - These properties `width` and `height` disturb to apply the size of Icons
+  - The property `fill` disturb to apply the icon color using CSS
+
+You will see this kind of codes when attaching svg file.
+
+```html
+<svg
+  xmlns="http://www.w3.org/2000/svg"
+  width="32px"
+  height="32px"
+  viewBox="0 0 64 64"
+>
+  <g fill="none">
+    <path d="..." fill="black" />
+  </g>
+</svg>
+```
+
+So remove those properties to apply the size and color.
+
+```html
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 64 64">
+  <g fill="none">
+    <path d="..." />
+  </g>
+</svg>
+```