While there is always the option to create a new theme, this is overkill for most minor style adaptations. For those minor changes, the recommendation is to include additional CSS into the page which changes the style of the respective tags of the SAPUI5 control. This allows complete, arbitrary changes of the visual design - after all it is the same technology that the UI5 controls use for their styling.
The main options are the following:
.addStyleClass("myStyle") on some control instances if you
want only those instances to look different from other instances - and then
write CSS code that refers to the normal classes/tags and to the CSS class you
just added.
When SAPUI5 is used in a standard way, which means loaded by
a<script> element in the <head> of a page, and all libraries declared in the
respective attribute of the script tag), it is sufficient to just add the custom CSS to any place after the SAPUI5
<script> element. SAPUI5 will insert its CSS links
immediately after the <script> tag, so any subsequent CSS will appear further down in the DOM and can thus
overwrite the SAPUI5 CSS.
However, it is important to understand the precedence rules of CSS: The order of appearance is not the only factor that determines which one of two or more conflicting rules wins. Actually it is only the least important factor. The most important (and maybe least known) factor is the specificity of the selector belonging to a rule.
For example,
if one rule says button {color:red;} to make all button texts red, and a second rule says div > button
{color:green;} to make all button texts, which are direct children of a <div> element, green, the
second rule always wins because it is more specific. The order of appearance in the DOM does not matter in this case. It would only
matter if both rules started with an equal selector, such as button{color:***}.
The order of loading is
completely irrelevant, only the position in the DOM counts in this case. If you load SAPUI5 without a <script> tag in the
<head>, or if you do not specify all used control libraries in the <script> tag, but
loaded some of them later on when the body was already loaded, you can still make sure a custom CSS appears further down in the DOM by
loading it with sap.ui.dom.includeStyleSheet(stylesheetUrl[, id])after loading SAPUI5 or the dynamically loaded control
library.
style property where I can make arbitrary
changes?A control usually does not map to one HTML element, but to a
whole tree of HTML elements. Whatever is set for the style property
would probably be added to the root element of this HTML tree, and only there, so
there is no style access to inner parts. If you just want to
override the height of a button, this would actually work. But as soon as a change
is a bit more complex, it will not work that easily. A more complex change is, for
example, adapting the height of a ComboBox control. The outer
<div> will get the proper height. And incidentally also
the <input> tag inside, as it has 100% height set. But the
dropdown arrow and the respective button-kind-of-thing has a fixed height, and the
whole control will look pretty broken then.
In other cases, when HTML elements that break the CSS inheritance chain are nested,
for example, <table> and font settings, you can change
style to a different font and text color, but it will simply do
nothing.
In general, we try to expose the obvious adaptation content in the API, for example,
the button height. But the less obvious adaptations might have to be supported from
inside the control to work properly, and
as
we cannot foresee and support everything you can do with a style
property, we raise the bar a little bit by requiring you to write
CSS (potentially using .addStyleClass(…) for the respective
control). With CSS you can do what you cannot do with a style
property: tweak the inner HTML components of a control.
Applications (at least the more traditional ones – currently this seems to be less of
a rule, but I'm not sure it will stay like this forever) need to conform to some
visual design guideline and, in general, it is not even desired that applications
change the TextField height or use font just the way they like. As
you can use CSS, UI5 still supports that, but we shouldn't make breaking the visual
design a rule in our official API.
If you want to change some styling and use control.addStyleClass(…)
to add a CSS class, but it does not seem to work, you first have to pin down exactly
what is not working:
You can check this by inspecting the HTML with your browser's developer tools.
sap.ui.core.Element). Only some of them support
addStyleClass.On all SAPUI5 application pages,
the HTML root tag of the DOM gets the additional attribute
data-sap-ui-browser where the value is the type and the current
browser version. When browser-specific CSS needs to be written, this attribute can
be used in CSS selectors.
html[data-sap-ui-browser*="sf"] button { /* this rule will only be applied if the current browser is ANY version of Safari */
padding-top: 0px;
}
There is not one single way to create a new theme, but there are several options. Which one you choose depends on several factors:
Depending on the answers it might be better to not even create a new theme but just adapt an existing one.