luci-theme-boostrap: cascade.css: Refactor unnecessary calc()

[griffenedge]

hsl lightness values are being unnecessarily calculated using calc(n / 255 * 100%). This PR replaces all instances of calc(n / 255 * 100%) with their calculated percentage values to 2 decimal points (e.g. calc(6 / 255 * 100%) -> 2.35%).

"You don’t need to use calc() to do math on numbers that you could do the math for." - https://jdsteinbach.com/css/where-to-use-css-calc-real-world/#for-math-on-compatible-numbers

• This PR is not from my main or master branch 💩, but a separate branch ✅
• Each commit has a valid ✒️ Signed-off-by: <[email protected]> row (via git commit --signoff)
• Each commit and PR title has a valid 📝 <package name>: title first line subject for packages
• Incremented 🆙 any PKG_VERSION in the Makefile
• Tested on: (architecture, openwrt version, browser) ✅
• ( Preferred ) Mention: @ the original code author for feedback
• ( Preferred ) Screenshot or mp4 of changes:
• Description: (describe the changes proposed in this PR)

[dannil]

Typo in commit message: luci-theme-boostrap -> luci-theme-bootstrap

[griffenedge]

Typo in commit message: luci-theme-boostrap -> luci-theme-bootstrap

Fixed

[systemcrash]

Merged. Thanks @griffenedge