How can I override inline styles with external CSS?

I have markup that uses inline styles, but I don't have access to change this markup. How do I override inline styles in a document using only CSS? I don't want to use jQuery or JavaScript.

HTML:

<div style="font-size: 18px; color: red;">
    Hello World, How Can I Change The Color To Blue?
</div>

CSS:

div {
   color: blue; 
   /* This Isn't Working */
}

The only way to override inline style is by using !important keyword beside the CSS rule. The following is an example of it.

div {
        color: blue !important;
       /* Adding !important will give this rule more precedence over inline style */
    }

<div style="font-size: 18px; color: red;">
    Hello, World. How can I change this to blue?
</div>

Important Notes:

• Using !important is not considered as a good practice. Hence, you should avoid both !important and inline style.

• Adding the !important keyword to any CSS rule lets the rule forcefully precede over all the other CSS rules for that element.

• It even overrides the inline styles from the markup.

• The only way to override is by using another !important rule, declared either with higher CSS specificity in the CSS, or equal CSS specificity later in the code.

• Must Read - CSS Specificity by MDN 🔗

inline-styles in a document have the highest priority, so for example say if you want to change the color of a div element to blue, but you've an inline style with a color property set to red

<div style="font-size: 18px; color: red;">
   Hello World, How Can I Change The Color To Blue?
</div>

div {
   color: blue; 
   /* This Won't Work, As Inline Styles Have Color Red And As 
      Inline Styles Have Highest Priority, We Cannot Over Ride 
      The Color Using An Element Selector */
}

So, Should I Use jQuery/Javascript? - Answer Is NO

We can use element-attr CSS Selector with !important, note, !important is important here, else it won't over ride the inline styles..

<div style="font-size: 30px; color: red;">
    This is a test to see whether the inline styles can be over ridden with CSS?
</div>

div[style] {
   font-size: 12px !important;
   color: blue !important;
}

Demo

Note: Using !important ONLY will work here, but I've used div[style] selector to specifically select div having style attribute

You can easily override inline style except inline !important style

so

<div style="font-size: 18px; color: red;">
    Hello World, How Can I Change The Color To Blue?
</div>

div {
   color: blue !important; 
   /* This will  Work */
}

but if you have

<div style="font-size: 18px; color: red !important;">
    Hello World, How Can I Change The Color To Blue?
</div>

div {
   color: blue !important; 
   /* This Isn't Working */
}

now it will be red only .. and you can not override it

<div style="background: red;">
    The inline styles for this div should make it red.
</div>

div[style] {
   background: yellow !important;
}

Below is the link for more details: http://css-tricks.com/override-inline-styles-with-css/