div {
    font-size: 7px;
    border: 3px dotted pink;
    background-color: yellow;
    color: purple;
}

body.mystyle > div.myotherstyle {
    font-size: 11px;
    background-color: green;
}

#elmnt1 {
    font-size: 24px;
    border-color: red;
}

.mystyle .myotherstyle {
    font-size: 16px;
    background-color: black;
    color: red;
}
<body class="mystyle">
    <div id="elmnt1" class="myotherstyle">
        Hello, world!
    </div>
</body>

What borders, colors, and font-sizes will the text be?

font-size:

! font-size: 24;, since #elmnt1 rule set has the highest specificity for the <div> in question, every property here is set.

border:

! border: 3px dotted red;. The border-color red is taken from #elmnt1 rule set, since it has the highest specificity. The other properties of the border, border-thickness, and border-style are from the div rule set.

background-color:

! background-color: green;. The background-color is set in the div, body.mystyle > div.myotherstyle, and .mystyle .myotherstyle rule sets. The specificities are (0, 0, 1) vs. (0, 2, 2) vs. (0, 2, 0), so the middle one “wins”.

color:

! color: red;. The color is set in both the div and .mystyle .myotherstyle rule sets. The latter has the higher specificity of (0, 2, 0) and “wins”.