Write lean easy-to-maintain CSS

There are many ways to lean and simplify SCSS. The first step is to establish if custom code is needed at all.

Flectra’s webclient has been designed to be modular, meaning that (potentially all) classes can be shared across views. Check the code before creating a new class. Chances are that there is already a class or an HTML tag doing exactly what you’re looking for.

On top of that, Flectra relies on Bootstrap (BS), one of the most complete CSS frameworks available. The framework has been customized in order to match Flectra’s design (both community and professional versions), meaning that you can use any BS class directly in Flectra and achieve a visual result that is consistent with our UI.


  • The fact that a class achieves the desired visual result doesn’t necessarily mean that it’s the right one for the job. Be aware of classes triggering JS behaviors, for example.

  • Be careful about class semantics. Applying a button class to a title is not only semantically wrong, it may also lead to migration issues and visual inconsistencies.

The following sections describe tips to strip-down SCSS lines when custom-code is the only way to go.

Browser defaults

By default, each browser renders content using a user agent stylesheet. To overcome inconsistencies between browsers, some of these rules are overridden by Bootstrap Reboot.

At this stage all “browser-specific-decoration” rules have been stripped away, but a big chunk of rules defining basic layout information is maintained (or reinforced by Reboot for consistency reasons).

You can rely on these rules.


Applying display: block; to a <div/> is normally not necessary.

div.element {
   display: block;
   /* not needed 99% of the time */


In this instance, you may opt to switching the HTML tag rather than adding a new CSS rule.

span.element {
   display: block;
   /* replace <span> with <div> instead
      to get 'display: block' by default */

Here’s a non-comprehensive list of default rules:

Tag / Attribute


<div/>, <section/>, <header/>, <footer/>

display: block

<span/>, <a/>, <em/>, <b/>

display: inline

<button/>, <label/>, <output/>

display: inline-block

<img/>, <svg/>

vertical-align: middle

<summary/>, [role="button"]

cursor: pointer;


:before {content: open-quote}
:after  {content: close-quote}

HTML tags

It may seem obvious, but the simplest and most consistent way of making text look like a title is to use a header tag (<h1>, <h2>, …). Besides reboot rules, mostly all tags carry decorative styles defined by Flectra.



<span class="o_module_custom_title">
   Hello There!

<span class="o_module_custom_subtitle">
   I'm a subtitle.


<h5 class="o_module_custom_title">
   Hello There!

<div class="o_module_custom_subtitle">
   <b><small>I'm a subtitle.</small></b>


Besides reducing the amount of code, a modular-design approach (use classes, tags, mixins…) keeps the visual result consistent and easily maintainable.

Following the last example, if Flectra titles’ design changes, these changes will be applied in the o_module_custom_title element too since it’s using an <h5> tag.

Utility classes

Our framework defines a multitude of utility classes designed to cover almost all layout/design/interaction needs. The simple fact that a class already exists justifies its use over custom CSS whenever possible.

Take the example of position-relative.

position-relative {
   position: relative !important;

Since a utility-class is defined, any CSS line with the declaration position: relative is potentially redundant.

Flectra relies on the default Bootstrap utility-classes stack and defines its own using Bootstrap API.

Handling utility-classes verbosity

The downside of utility-classes is the potential lack of readability.


<myComponent t-attf-class="d-flex border px-lg-2 card
{{props.readonly ? 'o_myComponent_disabled' : ''}}
card d-lg-block position-absolute {{props.active ?
'o_myComponent_active' : ''}}  myComponent px-3"/>

To overcome the issue you may combine different approaches:

  • in Qweb attributes, only use classes to be toggled on-the-fly;

  • use new lines for each attribute;

  • order classes using the convention [flectra component] [bootstrap component] [css declaration order].


      o_myComponent_disabled: props.readonly,
      o_myComponent_active: props.active
   class="myComponent card position-absolute d-flex d-lg-block border px-3 px-lg-2"