Which is more optimized code to put less pressure on a computer?

Recently, my concern is to make my website optimized so that it runs smoothly.

These are the codes:

.someThing {
border-radius: 15px;
width: 555px;
height: 347px;
border: 2px solid rgb(29, 30, 32);
...
}

.someThingElse {
border-radius: 15px;
display: none;
position: relative;
animation: fade 0.5s;
...
}

.someThing {
width: 555px;
height: 347px;
border: 2px solid rgb(29, 30, 32);
...
}

.someThingElse {
display: none;
position: relative;
animation: fade 0.5s;
...
}

.someThing, .someThingElse {
border-radius: 15px;
}

Do these such small differences make a website run smoother than before?

It doesn't make much difference, However it will reduce some bytes in downloading. So when the page is fetched at client side(In browsers from your server), it will be fetched faster(Because you have reduced the lines of border-radius.

This is matter of micro seconds, so you will not able to notice it or couldn't take much advantage of this.

For better readability of your code, the second option is good.