update readme

Author: chaseottofy

README.md

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+# invert-css-variables-ui
+
+A simple UI to bulk invert CSS variables. 
+Good for creating light/dark themes - just invert the colors and you're more than likely halfway there.
+
+- Uses [@invert-css](https://www.npmjs.com/package/invert-css), a package I made to invert the variables.
+
+## Usage
+
+Example input:
+
+```bash
+  --accent-1: #111;
+  --accent-2: rgb(255,170,204);
+  --accent-3: hsl(340,100%,88%);
+  --accent-4: #FFFFFF;
+```
+
+Example output:
+
+```
+  --accent-1: #eeeeee;
+  --accent-2: rgb(0,85,51);
+  --accent-3: hsl(160,100%,88%);
+  --accent-4: #000000;
+```
+
+- Invalid CSS variables/input will just output the invalid input. A console error will be logged.
+
+## Features
+
+- Maintains the variable names and output will have proper spacing.
+- Copy to clipboard.
+
+### Supported Color Formats
+
+- Hex (both short `#123` and long `#112233` formats)
+- RGB (`rgb(255,255,255)`)
+- RGBA (`rgba(255,255,255,0.5)`)
+- HSL (`hsl(120,100%,50%)`)
+- HSLA (`hsla(120,100%,50%,0.5)`)