developer.mozilla.org · ReferenceHow modern is MDN's CSS?
Checked 2 November 2026, the CSS on its home page as any visitor gets it. Sites change, so check it now for today's numbers.
Each weekly check lands in your dashboard.
1 old technique still there
Each with the modern way to replace it. Old CSS that works is fine; these are suggestions.
- Negative-margin guttersUse gap2
Also worth a look
These don't change the score, because modern code uses them too.
- !importantUse @layer54
- High-specificity selectorsUse @layer, :where()42
- ID selectorsUse classes, @layer3
- html or body prefixes for weightUse @layer1
- Repeated selector listsUse :is()1
- z-index of 1000 or moreUse the top layer (dialog, popover)1
- to stop single-word linesUse text-wrap: balance30
- Physical left and rightUse logical properties27
- Dark theme blocks that repeat valuesUse light-dark()4
What MDN's CSS is built with
Only what the page and its CSS show, with the evidencePartFoundEvidenceHow sure
- FontsInter, JetBrains Mono, BarlowCondensed-SemiBoldLoaded with @font-face from the site's own files.Very sure
- Site frameworkNot detectedNo framework's file paths in the page or its CSS.—
- PreprocessorCan't tellSass, Less and PostCSS leave no trace in the CSS a browser gets.—
Design tokens
CSS custom properties MDN defines, and how much of its CSS uses themTokens defined167custom properties
Colors from tokens100%167 of 167
Spacing from tokens10%10 of 97
Font sizes from tokens70%21 of 30
Dark modeYeswith prefers-color-scheme
What the 167 tokens hold
- Colors44
- Sizes and spacing26
- Fonts2
- Point at other tokens5
- Other values90
Main colors
- --color-white#fff
- --color-black#000
- --color-gray-90#f7f7f8
- --color-red-90#ffe6ea
- --color-orange-90#fef3eb
- --color-yellow-90#fef0c3
- --color-green-90#eaf6ef
- --color-blue-90#ecf4fe
- --color-purple-90#f7f0ff
- --color-white-alpha-25#ffffff40
Colors written out
Every color declaration uses a token.
transparent, currentColor and inherit don't count. Old CSS that works is fine; this is a map, not a score.Tokens a build step turns into plain values (Sass variables, most CSS-in-JS) never reach the browser, so they don't show here.