If your CSS codes are not applied properly so then you can try this

The !important is a way to make your CSS always be applied. A rule that has the !important property will always be applied no matter  CSS is in which document. So if you wanted to make sure that a property always applied So you can add the !important property to the tag. So, to make the paragraph text always blue , 

Example

<p>Will be Blue</p>

Sometime We need to change some css codes but we didn't find where the css is in which document and then few people's are add codes in cusom css( Wordpress ) or in any css file but if those codes are not worked . then you can use !important rule in end of your code like 

Example

p {      
      color : blue : !important;
}

If you are trying to change css but if css is already in other file and you didn't find where it is in which file . so then you can use custom css method for it but without !important rule your css will not 100% work. But if you can use !important so then css will always applied ,no matter if css is already have in any other file .

Example

<a id="testlink">Will be Blue</a>

Example ( like if this css is already in any file  )

#testlink 
{          
      color : red;
}

How to you can use !important in new same css code . let's See

Example

<a id="testlink">Will be Blue</a>

Example ( you just have to add !important , So then no matter if same css is already in backend  )

#testlink
{    
       color : blue !important;
}

I will make video tutorials Soon . Please comment below if you have any question . Thank you!