The first thing you’ll notice when you add a button to your website is that you’ve taken a trip back in time to 1999. The default button style is very old-fashioned and I can’t think of a use case where you’d want to keep it as it is. The good news is that there are loads of CSS styles that can make your buttons pop.

Remove Default

The first thing to do is remove the default buttons styles. It’s one of
those things that you might do 100 times, but you still need to
google every time. The CSS on how to remove the default style is
below.
button {
background: none;
color: inherit;
border: none;
padding: 0;
font: inherit;
cursor: pointer;
outline: inherit;
}
This will turn a button that looks like this
into one that looks like this

Color and Size

The next thing to do is to add your own styles. Bold colors with high
contrast text will help the button stand out. You will also probably
want to increase the button’s default size to make it more
prominent and add some padding. A call to action button might look like this.
button {
  background: none;
  color: inherit;
  border: none;
  padding: 0;
  font: inherit;
  cursor: pointer;
  outline: inherit;
}

Fonts

Fonts can be another great way to make a button look more attractive. I've added the font Oswald from Google Fonts. I like a bold sans-serif font on a button but you should choose whatever you like. Follow the instruction on Google to add the font to your project then insert 
font-family: "Oswald", sans-serif;
into the button CSS

Border-radius and Box-shadow

So far the button is standing out a lot more but to make it looks like
it seamlessly fits into the webpage it needs a couple more elements.
border-radius
and 
box-shadow
. The border-radius will round the
corners of the button. How much you want to do this is up to you. You
can just take the sharpness off the edges of the corners or turn it
into a full circle. 
box-shadow
as the name suggests will give your
button a shadow, which will give it a cool floating appearance. You
can do a lot with 
box-shadow
so read more about the properties
here
Button {
  background: red;
  color: white;
  border: none;
  padding: 20px;
  font: inherit;
  font-size: 1.6rem;
  cursor: pointer;
  outline: inherit;
  border-radius: 15px;
  box-shadow: 5px 5px 5px #000;
}

Hover and Active

Now our button is looking pretty good, it’s time to add some
functionality. You can add all sorts of styles with 
:hover
for when
the button is hovered over and 
:active
for when the button is
clicked. Some of the things you might want to do are:
For our button well change the brightness and box-shadow on hover and add indentation when it's clicked with 
::active
.
button:hover {
  filter: brightness(120%);
  box-shadow: 10px 10px 10px #000;
}

button:active {
  box-shadow: inset 2px 2px 10px #000;
}
For some awesome examples of what can be done by manipulating 
:hover
and 
:active
check out this website

::After

What other fun things can be done with buttons? You can combine 
::before
and 
::after
with 
:hover
or 
:active
to add extra content to the button. In the code below I’ve added 
::after
and 
:hover
with
CSS animation to create an underline when the button is hovered.
button::after {
  content: "";
  display: block;
  height: 5px;
  width: 0;
  background-color: #fff;
  transition: 0.1s width linear;
  margin: 0 auto;
}

button:hover::after {
  width: 100%;
}
Now it might be overkill having all of these effects but it shows you
what can be achieved.

Accessibility

There are a couple of important accessibility requirements to bear in mind.
Please please please use a 
<button>
tag. You can create something
that looks and works like a button using 
<div>
and 
<a>

but it doesn’t have the same semantic meaning as a button. This
means that screen readers won’t know that it is a button.
A button should look like a button. This is not just good for
accessibility but for anyone trying to navigate your site. With all
the styles you can add it’s important to remember that it should still be obvious that the element is a button. It should look
“clickable”. If it’s ambiguous it will cause confusion which is
not great for accessibility or UX. Adding some `box-shadow` to the
button often creates this effect.
Make the button easily visible. Much like you want good contrast between
text and the background, you also want to give your buttons lots of
contrast. It’s also important to show the status of a button. If a
button is going to remain depressed after clicking, to show that it is
active, consider adding a border or underline so that it can’t be
missed. This is important if the button shows the status of something
rather than if it’s just to submit a form, for example. Compare: