April 2025
Intermediate to advanced
1128 pages
32h 5m
Portuguese (Portugal, Brazil)
Content preview from CSS: O Guia Definitivo, 5ª Edição
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Capítulo 4. Especificidade, herança e a cascata
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Os Capítulos 2 e 3 mostraram como a estrutura do documento e os seletores CSS permitem aplicar uma grande variedade de estilos aos elementos. Sabendo que cada documento válido gera uma árvore estrutural, podes criar selectores que visam elementos com base nos seus antepassados, atributos, elementos irmãos e muito mais. A árvore estrutural é o que permite que os selectores funcionem e é também central para um aspeto igualmente crucial do CSS: a herança.
A herança é o mecanismo através do qual alguns valores de propriedade são transmitidos de um elemento para um elemento descendente. Ao determinar que valores devem ser aplicados a um elemento, um agente de utilizador tem de considerar não só a herança, mas também a especificidade das declarações, bem como a origem das próprias declarações. Este processo de consideração é conhecido como cascata.
Iremos explorar a inter-relação entre estes três mecanismos - especificidade, herança e cascata - neste capítulo. Por agora, a diferença entre os dois últimos pode ser resumida da seguinte forma: quando escrevemos h1 {color: red; color: blue;}, o <h1> fica azul por causa da cascata, e qualquer <span> dentro do <h1> também fica azul por causa da herança.
Acima de tudo, independentemente de quão abstratas as coisas possam parecer, continua! A tua perseverança será recompensada. ...
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