How to solve class inside section?

[toplisek]

How is possible that class will not be detected by browser.
<section id="section1" class="mycolour1">

If I add CSS: .mycolour1 it will work but
section#section1 .mycolour1 will not work. how to make it detected?

[brandozz]

That is because you are implying that the element that has the class mycolour1 is the child of the section element

section.mycolour1 should work fine.

[toplisek]

How to solve that class="mycolour1" will be applied only to specific ID like. section1 id="section1"?

[justa]

#section1.mycolour1 {}

But I'd advise you to stick to using .classes instead of #ids, it will save you specificity issues further down the line.

If you need to be more specific, include a class for .section1.mycolour1 {}

[lucy24]

How to solve that class="mycolour1" will be applied only to specific ID like. section1 id="section1"?

You don't need to. Just use the id by itself in CSS

#section1

The only exception is if there are pages where an element has this id but not the named class, and you don't want the styling to apply in those cases. That's when you go to justa's double-pronged approach:

#section1.mycolour1

Always remember that in CSS, each space means a new element.

.onething.otherthing

=
<element class = "onething otherthing">

.onething .otherthing

=
<element class = "onething">
{blahblah}
<element class = "otherthing">

Incidentally, is "mycolour1" a real class name, like "class = 'red'" or "class = 'cyan'"? Most of the time this is not the best choice for naming. Otherwise you'll end up, a few redesigns further, with

.red {color: blue;}
.green {color: gray;}

:)