'-webkit-text-size-adjust' is not supported by Chrome, Chrome Android, Edge 79+, Firefox, Safari, Samsung Internet. Add 'text-size-adjust' to support Chrome 54+, Chrome Android 54+, Edge 79+, Samsung Internet 6.0+.
'image-rendering: crisp-edges' is not supported by Edge. Add 'image-rendering: -webkit-optimize-contrast' to support Edge 79+.
Compatibility fix for mikutap.css
Fix a Pitfall "Prefixed CSS First" …
'animation' should be listed after '-webkit-animation' by Edge Chromium 90.0.818.51 DevTools.
3. Add favicon.ico - A necessary file for many browsers.
4. Improve for HTML5 grammar
index.html (8) There's a problem with the viewport value. It should be a comma-delimited list of valid viewport properties and values. Details: bad value for "user-scalable" (should be 'yes' or 'no').
Unsolved problem:
index.html (41) The "color" attribute is not valid here. This could be because "color" is a proprietary (non-HTML5) attribute. Instead of the "color" attribute, use the "color" CSS property. More: This "hr" tag uses one or more entirely obsolete (in HTML5) attributes which must not be used in HTML5 documents. The HTML5 obsolete attributes for "hr" include: "align", "color", "noshade", "size", and "width".
Ref to Prefixed CSS first | webhint documentation
Unsolved problem: