{"rowid": 206, "title": "Getting Hardboiled with CSS Custom Properties", "contents": "Custom Properties are a fabulous new feature of CSS and have widespread support in contemporary browsers. But how do we handle browsers without support for CSS Custom Properties? Do we wait until those browsers are lying dead in a ditch before we use them? Do we tool up and prop up our CSS using a post-processor? Or do we get tough? Do we get hardboiled?\nPreviously only pre-processing tools like LESS and Sass enabled developers to use variables in their stylesheets, but now Custom Properties have brought variables natively to CSS.\nHow do you write a custom property? It\u2019s hardly a mystery. Simply add two dashes to the start of a style rule. Like this:\n--color-text-default : black;\nIf you\u2019re more the underscore type, try this:\n--color_text_default : black;\nHyphens or underscores are allowed in property names, but don\u2019t be a chump and try to use spaces. \nCustom property names are also case-sensitive, so --color-text-default and --Color_Text_Default are two distinct properties.\nTo use a custom property in your style rules, var() tells a browser to retrieve the value of a property. In the next example, the browser retrieves the black colour from the color-text-default variable and applies it to the body element:\nbody {\n    color : var(--color-text-default); \n}\nLike variables in LESS or Sass, CSS Custom Properties mean you don\u2019t have to be a dumb mug and repeat colour, font, or size values multiple times in your stylesheets. Unlike a preprocessor variable though, CSS Custom Properties use the cascade, can be modified by media queries and other state changes, and can also be manipulated by Javascript.\n(Serg Hospodarets wrote a fabulous primer on CSS Custom Properties where he dives deeper into the code and possible applications.)\nBrowser support\nNow it\u2019s about this time that people normally mention browser support. So what about support for CSS Custom Properties? Current versions of Chrome, Edge, Firefox, Opera, and Safari are all good. Internet Explorer 11 and before? Opera Mini? Nasty.\nSound familiar?\n\n  Can I Use css-variables? Data on support for the css-variables feature across the major browsers from caniuse.com.\n\nNot to worry, we can manually check for Custom Property support in a browser by using an @support directive, like this:\n--color-text-default : black;\n\nbody {\n    color : black;  \n}\n\n@supports ((--foo : bar)) {\n    body {\n        color : var(--color-text-default); \n    }\n}\nIn that example we first set body element text to black and then override that colour with a Custom Property value when the browser supports our fictitious foo bar variable.\nSubstitutions\nIf we reference a variable that hasn\u2019t been defined, that won\u2019t be a problem as browsers are smart enough to ignore the value altogether. If we need a cast iron alibi, use substitutions to specify a fall-back value.\nbody {\n    color : var(--color-text-default, black); \n}\nSubstitutions are similar to font stacks in that they contain a comma separated list of values. If there\u2019s no value associated with a property, a browser will ignore it and move onto the next value in the list.\nPost-processing\nOf course we could use a post-processor plugin to turn Custom Properties into plain CSS, but hang on one goddam minute kiddo.\nHaven\u2019t we been down this road before? Didn\u2019t we engineer elaborate workarounds to enable us to use \u2018advanced\u2019 CSS3 properties like border-radius, CSS columns, and Flexbox in the past? We did what we had to do to get the job done, but came away feeling dirty.\nI think there\u2019s a better way, one that allows us to enjoy the benefits of CSS Custom Properties in browsers that support them, while providing an appropriate, but not identical experience, for people who use less capable browsers. Guess what, I\u2019ve been down this road before too. \n2Tone Stuff & Nonsense\nWhen Internet Explorer 6 was the big dumb browser everyone hated, I served two different designs on my website. \nFor the modern browsers of the time, mod arrows and targets were everywhere in glorious red, white, and blue, and I implemented all of them using CSS attribute selectors which were considered advanced at the time:\n[class=\"banner\"] {\n    background-colour : red; \n}\nInternet Explorer 6 ignored any selectors it didn\u2019t understand, so people using that browser saw a simpler black and white, 2Tone-based design that I\u2019d implemented for them using class selectors:\n.banner {\n    background-colour : black; \n}\n\n[class=\"banner\"] {\n    background-colour : red; \n}\n\nYou don\u2019t have to be a detective to find out that most people thought I\u2019d lost my wits, but Microsoft even used my website as a reference when they tested attribute selectors in Internet Explorer 7. They did, as I suggested, \u201cStomp to da betta browser.\u201d\nDumb browsers look the other way\nSo how does this approach relate to tackling any lack of support for CSS Custom Properties? How can we take advantage of them without worrying about browsers with no support and having to implement complex workarounds, or spending hours specifying fallbacks that perfectly match our designs?\nTurns out, the answer is built into CSS, and always has been, because when browsers don\u2019t know what they\u2019re looking at, they look away. \nAll we have to do is first specify values for a simpler design first, and then follow that up with the values in our CSS Custom Properties:\nbody {\n    color : black;\n    color : var(--color-text-default, black); \n}\nAll browsers understand the first value (black,) and if they\u2018re smart enough to understand the second (var(--color-text-default)), they\u2019ll use it and override the first. If they\u2019re too damn stupid to understand the custom property value, they\u2019ll ignore it. Nobody dies.\nRepeat this for every style that contains a variable, baking an alternative, perhaps simpler design into your stylesheets for people who use less capable browsers, just like I did with Stuff & Nonsense.\nConclusion\nI doubt that anyone agrees with presenting a design that looks broken or unloved\u2014and I\u2019m not advocating for that\u2014but websites need not look the same in every browser. We can use substitutions to present a simpler design to people using less capable browsers.\nThe decision when to start using new CSS properties isn\u2018t always a technical one. Sometimes a change in attitude about browser support is all that\u2019s required. So get tough with dumb browsers and benefit from all the advantages that CSS Custom Properties offer. Get hardboiled.\nResources:\n\nIt\u2019s Time To Start Using CSS Custom Properties\u2014Smashing Magazine\nUsing CSS variables correctly\u2014Mike Riethmuller\nDeveloping Inspired Guides with CSS Custom Properties (variables)\u2014Andy Clarke", "year": "2017", "author": "Andy Clarke", "author_slug": "andyclarke", "published": "2017-12-13T00:00:00+00:00", "url": "https://24ways.org/2017/getting-hardboiled-with-css-custom-properties/", "topic": "code"}